GMC Debuts Industry “First” Features And Adds A New 4x4 Model To Its 2020 Heavy-Duty Pickup Offerings

Bigger. Bolder. Quieter. Quicker. Smoother. Stronger. Smarter. Those are just a few of the words that came to mind when we wrapped up a couple of days behind the wheel of the '20 GMC Sierra HDs, both gas and diesel. The four-wheel-drive Crew Cab 2500 and 3500 dualies we drove made it clear that GM's halo brand on the truck side is determined to keep leading the way on the technology and towing fronts, all the while refining ride and handling.

As we've previously covered in detail about the new Chevrolet Silverado HDs, the heavy-duty '20 GMC Sierra 2500/3500s share the same chassis, underpinnings, and drivetrain. For example, the new chassis of the Crew Cab with the standard bed now sports a wheelbase of 158.9 inches compared to the '19's 153.7-inch wheelbase. It's also 1.5 inches wider with a 1-inch-wider rear track.

Along with the bigger chassis comes a bigger body and new bed box. The body is more than 10 inches longer, nearly 2 inches taller and wider; the hood sits higher; the grille is bolder; and the cab is more spacious, with 3 inches of added rear legroom—and the most headroom in the heavy-duty pickup market.

The bed is more spacious, too. In fact, this marks the first time the HDs and 1500s have different beds, with the HDs having a 3-inch-longer floor in the standard bed and a usable width in some areas that's nearly 7 inches wider, giving the new box almost 9 cubic feet more volume than the previous model.

Power DeliveryPower comes from either the new 401hp 6.6L gas V-8 (built exclusively for use in the new HDs) that makes 464 lb-ft of torque or the optional 6.6L Duramax LP5 (445 hp/910 lb-ft of torque) turbodiesel that's a carryover from last year. GM says the direct-injected gas V-8, which is backed with the 6L90 six-speed automatic, provides 18 percent more towing capacity than the 6.0L it replaces.

An even greater change in power delivery and towing capacity comes from pairing the LP5 Duramax with the all-new 10-speed Allison. As we noted in the earlier article, the Allison-badged 10L1000 10-speed is built in-house by GM. What many readers may not know is that General Motors owned Allison Transmission since 1929, right on through when the six-speed version of the Allison 1000 came out in 2006. Then in 2007, the two companies parted ways.

According to David Ames, he and about half the engineers who developed the Allison 1000 stayed on with GM. A decade later, those engineers and Ames, now the assistant chief engineer of GM's pickups and lead on the automatics, helped design the 10L1000. All through the development process they collaborated with some of their old workmates at Allison in testing and validating the new transmission so it could carry the Allison Transmission badge. (By the way, the new 10-speed automatic in the '20 1500s is an entirely different transmission than the Allison 10L1000.)

The end result is a fast-shifting, close-ratio, intelligent 10-speed that puts the LP5's power to the ground in a manner that GM says outperforms competitors' diesels with higher torque outputs. The two biggest contributors to the power delivery, according to Ames, are the use of a variable pump and lock-up in First gear.

Lock-up Torque"Basically, you're bypassing the torque converter when you lock-up, and it gets rid of a lot of the heat," Ames explains. "Under hard acceleration or towing, the Allison 1000 wouldn't lock-up the torque converter until it was in Third or sometimes Fourth gear. That generated a lot of heat and loss of power delivery. This transmission [10L1000] will lock up in First gear [in Tow/Haul mode] and put all the torque to the ground."

Ames says they used "the best performance parts we know of in clutches, clutch packs, pumps, and solenoids" when it came to the redesign, and they built it to withstand a lot more power than the current LP5 delivers. "Now we've got six clutches instead of five, four planetaries instead of three, stronger gearsets, and the newest technology as far as solenoids and controls. It's stout."

Auto 4WDIt's also shorter, and the case is stronger than the old Allison. That's because the 10L1000 no longer uses an adapter to bolt up to the transfer case. Instead, the transmission bolts directly to the equally new Magna Powertrain Autotrac MP3025 transfer case.

The Autotrac two-speed transfer case has been used in the light-duty pickups for years, but never in a 2500/3500 until now. The MP3025 has heavier-duty internals than the MP3024 used in the 1500s, so it can withstand the delivery of the LP5's full torque in every gear. This also marks an "industry first" in the heavy-duty pickup market for an electronic, automatic four-wheel-drive T-case.

Like the Autotrac system used in the 1/2-tons, the MP3025 provides automatic torque transfer (0 to 50 percent) to the front differential when the "Auto" button on the left side of the dash is pushed. The Auto-mode can be engaged at any time and is said to be ideal for most driving conditions. The other modes are: 2WD, where 100 percent of the torque goes to the rear axle; 4-Hi splits torque 50/50 front/rear; and 4-Lo splits the torque 50/50 with a 2.68:1 gear reduction. Shifting in/out of 4-Hi or 4-Lo has to be done when the truck is stopped.

The power delivery goes through bigger driveshafts than the previous trucks and into either American Axle or GM Corporate differentials, according to Tim Herrick, the truck platform's chief engineer. Axlehousings run 11.5-inch ring gears on all the HDs except the dual-rear-wheel models, which have 12-inch ring gears. Axle ratios across the GM HD line are now limited to just one: 3.42s for the Duramax and 3.73s for the 6.6L gas engine. Both are available with the Eaton MLocker/G80 mechanical locking rear differential.

Heavy Duty AT4GMC brought out its "off-road" AT4 model in the '19 1500s, and that was followed up with a similar version in the HDs for 2020. The HD AT4 is easily distinguished from its brethren by its bumpers and a grille surround finished in body color, a black chrome grille, the red towhooks, and a black leather interior. It's priced between the mid-level SLT trim and the high-end Denali. It's a fine package and our favorite among the GMC HDs we drove.

The HD AT4 comes standard with Michelin all-terrain tires on 18-inch wheels, but the 2500HD Crew Cab we drove had 34-inch LT275/65R20 Goodyear TrailRunner ATs mounted on optional 20-inch wheels ($1,100). While the 1500 AT4s have a 2-inch lift, the HDs already sit several inches higher than their smaller counterpart, so no lift was needed to slip on the 34-inch off-road treads.

The AT4-specific black leather interior is just as nice as the exterior, with its darkened trim; AT4 badging stitched into the headrests; all-weather floor liners; and dark-tinted and textured aluminum finishes on the steering wheel, center stack and sill plates.

What really makes the AT4 shine, in our opinion, is the suspension tuning and supporting technologies that give it a distinct edge off-pavement over the rest of the GMC HDs. The AT4 uses custom-tuned Rancho monotube high-pressure gas shocks (the standard shocks are twin-tube non-gas) matched with more progressive-rate rear springs and torsion bars than those found under the other models, and it comes with a 33.6mm front antisway bar for better handling and body control.

According to Herrick, the suspension engineering team spent a "significant amount of time" on all the '20 HDs, focusing on tuning the front to rear to reduce "head toss" and to provide level ride height even with a load in the bed. The AT4 received even more suspension tuning attention to meet the engineering team's standards for such use.

Our short amount of time driving off-pavement and tossing the 2500 AT4 Crew Cab around a gravel field road showed GM's work appears to be done well. The AT4 suspension isn't jittery, and the truck behaves admirably over dips and bumps at speed—even with 1,200 pounds of logs strapped down in the bed.

The AT4's off-road capabilities are further enhanced with the incorporation of GM's Traction Select System that features multiple Off-Road modes in which shift points, traction control, throttle, and other computer-controlled aspects are tailored to different off-road driving conditions. Hill Descent Control, Hill Start Assist, a "segment-exclusive" 15-inch diagonal Head-Up Display with Off-Road Inclinometer, and HD Surround Vision for low-speed views of the truck's immediate surroundings add to the AT4's coolness.

We expect this package to be just as attractive and functional on the jobsite as it is on weekend adventures.

Six-Way TailgateThe option list of comfort, convenience, and safety packages for the '20 GMC HDs and 1500s is expansive. But two features that caught our eye that are exclusive to GMC are bed related—the six-function MultiPro Tailgate that's available on both the Sierra HDs and 1500s, and the CarbonPro bed available on select models of the 1/2-tons.

The MultiPro is a tailgate within a tailgate with a fold-out load stop/step, allowing it to be configured six different ways to meet one's needs. Configurations include a regular powered tailgate, a chest-high middle tailgate, a mid-level step to the bed, and an extension to the upper bed. In addition to all that, GMC offers a Kicker Audio option to make the drop-down step/seat your own private sound system. The MultiPro tailgate is truly impressive in both function and form, especially to those who use their pickup beds on a daily basis.

As for the exact cost, it's hard to determine, because the MultiPro is "standard" on the Sierra SLT, AT4, and Denalis (both 1500s and HDs), and at this time GMC hasn't listed the price of it as a stand-alone option for the Base, SLE, or Elevation models.

Carbon-Fiber BedLikewise, the price of the carbon-fiber-reinforced plastic (CFRP) CarbonPro bed is hard to determine because it's currently available only as part of an all-inclusive $11,840 "CarbonPro Edition" package on the Sierra 1500 AT4 and Denali. (Note: This package includes nearly every option GMC offers in the 1500s, including the CarbonPro bed and MultiPro tailgate to the 6.2L V-8 to performance exhaust to all the technology packages.)

The CarbonPro bed is a significant step up the durability-and-design ladder from other "composite" bed offerings because it's made up of parts created using molded thermoplastic resin impregnated with inch-long strands of carbon fiber. GM touts the CFRP bed as being six times stronger than the standard stamped-steel bed and 60 pounds lighter, making it the most durable and lightest pickup bed currently on the market.

Bed durability may not seem like a big deal to many, but when it comes time to resell or trade in a pickup, one of the biggest "value" factors is the condition of the bed. The CarbonPro doesn't require a bedliner or spray-on coating to protect it. It's already impervious to the deteriorating effects of UV light and the hardest of knocks from daily use and abuse.

Pulling Their WeightLike the Chevrolet counterparts, the '20 GMC Sierra 2500/3500 HDs far surpass the towing and load-carrying abilities of the previous generation. The new Allison 10-speed, the new 6.6L gas engine, the new chassis and refined suspension, improved aerodynamics and cooling, along with the new body and grille changes have pushed these trucks to, or very near, the best in class when it comes to overall trailering performance.

For example, the '20 Crew Cab 3500 Duramax dualie 4x4 is rated to tow a fifth-wheel or gooseneck trailer up to 31,400 pounds, while the single-rear-wheel version can pull 21,500 pounds. Similarly, a 2500HD Crew Cab 4x4 diesel can handle an 18,500-pound trailer, while the gas version is rated at 16,900 pounds.

Towing in the conventional mode (using the OEM receiver hitch), the diesel 3500s are rated at 20,000 pounds and the 2500HDs are 18,500, with the gas models coming in at 16,300 and 14,500 pounds, respectively.

A New WorldIn addition to being true workhorses, the '20 GMCs are noticeably quieter inside and out than the previous models, with a remarkable array of technology available that makes time behind the wheel more pleasant and safer than ever before. GMC's addition of the AT4 extends that sense of security, comfort, and performance off-road. It's a whole new world compared to pickups that are even a few years old.

Camera systems let you "see through" trailers and eliminate blind spots; computers lead you through pre-trip trailer checks; sophisticated electronics control traction and braking and alert the driver to potential safety hazards on- and off-road; the gas and diesel drivetrains provide more power and higher fuel efficiency; and the navigation and entertainment systems keep you connected, informed, and entertained. Life behind the wheel doesn't get much better.

As for pricing, a nicely equipped '20 GMC Sierra 1500 AT4 Crew Cab 4x4 with the 5.3L EcoTec3 V-8 will set one back around $54,000. A loaded Sierra 2500 Crew Cab AT4 Duramax like we drove comes in around $77,000. Step up to a full-featured '20 Sierra 2500 Denali Duramax Crew Cab 4x4, and the MSRP is pushing $79,600.

Quick Specs (as tested)Vehicle/model: '20 Sierra 2500 4WD Crew Cab AT4 SRW

Base price: $57,700

As tested: $77,210

Engine: 6.6L Duramax V-8 turbodiesel

Rated hp/torque (lb-ft): 445/910

Transmission: Allison 10L1000 10-speed

Transfer case: Magna Powertrain Autotrac MP 3025

4WD system: A4WD, 2-Hi, 4-Hi, Neutral, 4-Lo

Low range ratio: 2.68:1

Frame type: Ladder

Suspension, f/r: Short long arms independent suspension with torsion bars/Semi-elliptic three-stage multi-leaf spring; Rancho monotube shocks; 33.6mm front antisway bar

Axle ratio: 3.42:1

Max crawl ratio: 41.6:1

Steering: Hydraulic power recirculating ball with digital steer assist

Brakes, f/r: 14x1.6-in disc with twin-piston pin-slider caliper with ABS and StabiliTrak/14 x1.30-in disc with twin-piston pin-slider caliper with ABS and StabiliTrak

Tires: LT275/65R20 Goodyear TrailRunner AT

Wheelbase (in): 158.9

Length (in): 250

Height (in): 79.8

Width (in): 81.9

Base curb weight (lb): 7,467

Payload (lb): 3,597

Max towing capacity (lb): 18,500

Fuel capacity (gal): 36