2020 GMC Sierra HD: Towing the Competition

Strong points
  • Best-in-class towing capacity
  • Best-in-class interior room
  • Diesel engine available in AT4 trim
Weak points
  • Questionable interior design and quality
  • Gas engine not available with 10-speed box
  • Big price (Denali and AT4 models)
Full report

JACKSON HOLE, Wyoming—The heavy-duty pickup segment has become so competitive that the latest product on the market automatically becomes the king of the hill.

This year has been a historic one. It all started with the 2019 Ram Heavy Duty and its 1,000 pound-feet of torque. Then, Ford made a promise that its updated 2020 Super Duty will be even more powerful and capable than its predecessor when it launches this fall.

As we write these lines, however, the 2020 Chevrolet Silverado HD and GMC Sierra HD are the towing champions. After putting the former to the test on the roads of Oregon, we headed to the Grand Teton National Park in Wyoming for a crack at the latter.

Photo: William Clavey

Standing Out

GMC is trying to develop a unique identity within the General Motors family. It recently announced the expansion of the AT4 sub-brand to all GMC models, while its all-new Sierra 1500 features exclusive technologies such as the CarbonPro cargo bed and the MultiPro tailgate.

The Sierra HD takes things to another level. Of course, it’s built on the same chassis as the Silverado HD, which is an extended and reinforced version of the light-duty pickups. The powertrain options are the same, too. However, GMC has added a ton of details and upgrades that are substantial enough to set its workhorse apart from the platform-sharing, bowtie-wearing model.

The most notable is the first-ever AT4 variant in the Sierra HD lineup. Featuring underbody skid plates, tow hooks, a two-inch lift kit with Rancho shocks, an Eaton locking rear differential and black-painted 18-inch wheels wrapped in off-road tires, the 2020 GMC Sierra HD AT4 is a direct threat to the new Ram 2500 Power Wagon and the upcoming Ford Super Duty Tremor.

Photo: William Clavey

GMC has an edge over both rivals, which rely on a gasoline V8. The AT4 is available with a 6.6-litre Duramax turbo-diesel engine that’s significantly improved for 2020. This proven powerplant now delivers 445 horsepower and 910 pound-feet of torque through a 10-speed Allison transmission, giving the Sierra HD best-in-class towing capacity of 35,500 pounds (16,102 kilograms) and making it the strongest off-road pickup on the market—at least for the time being.

A gasoline V8 can also be specified with the big GMC, mind you. It’s a new 6.6-litre unit rated at 401 horsepower and 464 pound-feet of torque. Mated to a six-speed transmission, it can tow up to 17,400 pounds (7,892 kilograms), which is not even half the capacity of the diesel.

Photo: William Clavey

Rocks, Mud and Big Trailers

The GMC team at the media event had quite a few exercises in store for us, one of which was an off-road course to test the new AT4 model. We had to climb up a hill covered in big rocks, then tackle uneven terrain and muddy sections.

To be clear, the AT4 aims to fill a void between conventional half-ton pickups and hardcore machines like the Ford F-150 Raptor, so this was exactly the kind of challenge the intended customer revels in.

After that came two towing sessions. The first one involved pulling a load of about 20,000 pounds (9,071 kilograms) on the winding roads of Wyoming. The second and most important towing exercise was to validate the maximum 35,500-pound capacity with a Sierra 3500HD Dually.

Photo: William Clavey

In both cases, the truck never failed. Strong and smooth at all times, the Duramax under the hood impressed us with its brute power and torque, not to mention the virtually non-existent turbo lag compared with the Cummins engine in the Ram Heavy Duty.

What’s more, the 10-speed transmission is extremely well suited to massive workloads. While pulling a trailer up a hill, downshifts were silky smooth. The same cannot be said about the Ram and its six-speed box. GM engineers did their homework and it shows.

Photo: William Clavey

Beauty is Not Inside

The rudimentary dashboard design of the 2020 GMC Sierra HD is a letdown. Even in AT4 trim starting at $92,113, material quality is poor. Sure, you can move up to the leather-clad, chrome-accented Denali model, but the cabin still feels relatively cheap no matter what. The good news is that GM plans to upgrade its pickup interiors very shortly.

On a positive note, the various controls are conveniently positioned and there is no shortage of space. The extended chassis results in a humongous back seat with plenty of room for the legs, shoulders and head. Visibility is excellent thanks to the lowered beltline, while the infotainment system remains one of the best in the industry by far, along with the rest of the GM family. The interface is a model of simplicity and straightforwardness.

The Sierra HD also adds towing assist features like the upgraded ProGrade Trailering System (optional). Using a tailgate-mounted camera and an available accessory camera mounted on the rear of the trailer, the system creates a composite image allowing you to virtually see through the trailer—perfect for parking lots and other tight areas

Photo: William Clavey

The Verdict

The 2020 GMC Sierra HD is finally positioning itself as a unique offering and a towing leader in this highly competitive segment. With an outstanding off-road variant, exclusive features such as the multi-function tailgate and unbreakable carbon fibre bed, plus a much more attractive design than its cousin from Chevrolet, GMC’s new monster stands tall and defiant.

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