2020 GMC Sierra 2500 HD Diesel Towing Review: Powerful Hauler, Dull Package

910 pound-feet of torque is an eye-popping number. Too bad the rest of the truck isn't.

2020 GMC Sierra HD Denali
Darcy Bacha

With the U.S. economy on an upward slope for the last decade, the number of toys for the campground, lake, ocean, desert, off-road park, racetrack, or even airfield nowadays has skyrocketed. And like good Americans, we need a commensurate number of pickup trucks with which to tow them. Even if your average crossover can pull an ATV or two, heavy-duty pickups remain the champs, and now there's a new player bursting onto the field with as much tact as the Kool-Aid man: The 2020 GMC Sierra 2500 HD Diesel.

Of course, measuring a truck's capability with a bed of air is useless even if it's a growing use case. So we hitched up the Sierra 2500 HD Diesel to a variety of trailers ranging from luxurious fifth-wheel campers to utilitarian boxes and hauled them all around the wide-open roads of Jackson Hole, Wyoming to see how it stacks up.

2020 GMC Sierra 2500 HD Diesel, By the Numbers

  • Base Price: $69,185 (AT4 Crew Cab 4WD)
  • Powertrain: 6.6-liter turbodiesel V-8 | 445 horsepower, 910 pound-feet of torque | 10-speed automatic transmission | Rear-wheel drive with on-demand four-wheel drive
  • Max Towing Capacity: 18,500 pounds
  • Max Payload Capacity: 3,597 pounds
  • Fuel Economy: Not available
  • Quick Take: It's got all the capability you'd expect from a $70,000-plus heavy-duty truck, but still not enough to beat Ford and Ram.
Jerry Perez
GMC

Polarizing by nature, the 2500 HD sports a gargantuan front fascia dominated by an extra-large grille and two massive headlight housings. In the back, GMC's new optional MultiPro tailgate lends a vaguely futuristic feel to the boxy design language. In all fairness, the truck is more handsome in person than it is in photographs, but it takes a while to get used to. In Denali trim, the majority of the truck is surrounded by chrome accents that turn it into a rolling mirror on a sunny day—call it a Cowboy Cadillac. In the AT4 off-road spec, the chrome is replaced by shiny black plastic and red tow hooks that complement its welcomely rugged look.

Under the hood, a Duramax 6.6-liter V-8 turbodiesel engine (which fits in the bay like an elephant in an NYC hotel room) cranks out 445 horsepower and 910 pound-feet of torque. Attached to it, a 10-speed Allison automatic transmission. The result? A maximum towing capacity of 18,500 pounds in 2500 crew cab configuration. Opt for the big boy 3500 dually regular cab and that number skyrockets to 35,500, well beyond what a non-commercial driver's license allows.

Jerry Perez

Two Trailers, One Experience

Our first go at the new 2500 HD Diesel came with a 36-foot Keystone Cougar travel trailer hooked up via a fifth-wheel setup. Tipping the scales at approximately 14,000 pounds, it was a worthy challenge for the Sierra. Also, let's not forget that while trucks nowadays are more capable and tricked-out than in the past, all the gadgets in the world aren't a replacement for skill behind the wheel when you're hauling seven tons. After performing a lights-check through the Sierra's own trailering app on the infotainment screen—a feature we truly believe can save marriages—we set off into the Grand Tetons, starting at over 6,200 feet above sea level. All the better to test the turbodiesel's might.

The weight behind the truck announced itself immediately under acceleration, but the quiet and relentless Duramax surged through the inertia and cruised effortlessly at speed. If you jumped in blindfolded, you might not even guess there was a 36-foot trailer out back. But slowing down was a different story. Even with a diesel exhaust brake that makes you feel like a big boy trucker, stopping performance with a heavy load wasn't great. Shaving speed from 70 miles per hour ahead of a full stop took a longer distance than expected and prompted a nervous double-take at the speedo. The brake pedal felt too spongy and offered little bite until the very end of the stroke, which isn't exactly reassuring when towing a heavy trailer.

Jerry Perez

Once rolling on the highway, the Sierra's available 15 cameras came in handier than we ever expected. Yes, die-hard truck owners can make fun of these and whine about how they've towed bigger loads without this silliness, but the truth is that if something can be done safer thanks to modern technology, then we should be all for it. Whenever a turn signal is activated, the rear-facing camera on that side is projected on the infotainment screen to provide full-length visibility.

And while the side and backup cameras are neat (and so are the wireless cameras one can install inside the trailer), it's the "invisible trailer" technology that is by far the coolest and most helpful. At the touch of a button, a camera mounted above the truck's rear windshield links up with others (including one on the back of the trailer) to stitch together an image that makes the trailer "disappear." This was especially helpful when passing on multi-lane highways. We've towed cross-country with crappy wireless cameras where video feeds lag several seconds behind, and the Sierra's system is an excellent improvement.

Jerry Perez
GMC

Next we swapped our camper for a shorter but considerably heavier box trailer hooked up to the rear hitch rather than the fifth-wheel bed attachment. At 18,000 pounds, it pushed the Sierra 2500 HD Diesel much closer to its limit—and this time, that weight was centered on the tongue rather than the rear axle, a far less stable arrangement.

The strain on the engine was noticeably higher, but acceleration was still surprisingly quick and plenty for highway merging. GMC credits the 10-speed auto, claiming it manages torque better than the competition—more specifically, reps called out the Ram Heavy Duty. GMC also showed a graph claiming that the Sierra can tow an 18,000-pound trailer from zero to 60 in 19.9 seconds compared to the Ram's 21.9 even though the Ram pumps out 90 more pound-feet of torque.

Jerry Perez
Jerry Perez

That much weight also hits the handling pretty hard. It took a leap of faith to trust that the front independent suspension (Ram and Ford still use solid front axles on their HD trucks) could handle the weight loading up behind us as we entered curve after curve, but it managed well enough considering we were right at towing capacity. Here the lackluster mechanical brakes again proved a weak spot. Unlike with the Ram 2500 and Airstream trailer we recently towed around the Black Hills of South Dakota, the lack of feedback in the Sierra's pedal forced caution. In contrast, the diesel exhaust brake seemed to perform better and better as our load weight increased.

Sierra HD's Interior Fails to Impress

GMC

Confidence gained, we began paying attention to the things around us—and no, not the staggering Grand Tetons, but the GMC Sierra's worst-in-class interior. Cheap-to-the-touch dark plastics abound throughout the cabin, including in main focal areas like the center console and the dashboard directly in front of the passenger. The design is best described as blobby. We were also disappointed by the lack of height-adjustable seatbelts or power-adjustable pedals—so whether you're five or seven feet tall, you'll just simply have to adjust to GMC's idea of the right driving position. Thankfully, the seats are still quite nice.

But the biggest miss might be the lack of an adaptive cruise control for those long highway trips. You can get a camera for a rearview mirror and an origami tailgate, but not adaptive cruise control? What is that, GMC?

Jerry Perez

Rearview mirror camera.

It’s not all doom and gloom for the Sierra because it does beat its rivals in some areas. For example, the ride quality is phenomenal in part thanks to the IFS, offering a quieter cabin with fewer vibrations at the wheel and pedals than Ford or Ram. The admittedly-cheesy tailgate is actually pretty cool to use in some of its more practical configurations. The 2500 HD in AT4 trim is better-looking than the 2020 Ford Super Duty with the Tremor Off-Road package and more civilized than the Ram Power Wagon. Lastly, the extensive trailering technology options also set GMC apart.

But in the end, the 2020 GMC Sierra 2500 HD Diesel is merely a decent truck in an extremely strong market. Stack it up against the outgoing Sierra HD generation and there's a clear evolution, incremental increases in most areas that are designed more to reassure the repeat customer than bring in new blood. Judged to the standards set by Ram and Ford, the Sierra's technical merits are mostly overshadowed by poor execution and disappointing packaging. That's not going to win the day in an arena this competitive.