2020 GMC Sierra HD Review: The Classiest Tow Truck in Existence

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Before kicking off its drive program for the 2020 GMC Sierra HD this summer in the wilds of Wyoming, an engineer cited a recent survey the manufacturer had completed about towing. Of the 7,000 respondents, 57 percent claimed they got nervous or anxious while towing.

“The other 43 percent lied,” the rep quipped.

Mitigating towing-related stress for everyone from noobs to veteran haulers, then, was high on the hit list for GMC engineers when they were sorting out the brand’s new heavy-duty.

The Good: Exterior-wise, it’s quite a handsome truck. Unlike its cousin, the Chevrolet Silverado HD, it’s got both presence and appeal. Credit that ginormous, intimidating grille, sure; but engineers also worked to bring bigger proportions to the Sierra HD, and in the truck world, bigger is always better.

If you’re looking for a premium feel, opt for the Denali trim, which sees the addition of heaps of chrome in nearly every conceivable place. For those who shy away from shimmering opulence, there’s the AT4, which blacks out all the brightwork, imbuing the Sierra with a satisfyingly sinister appearance. The AT4 also brings some decent heat for off-road enthusiasts, thanks to a two-inch lift over other Sierra models, Rancho shock absorbers, an Eaton locking rear differential, and extra skid plates.

The innovative six-function MultiPro tailgate is also worth chalking up in the positive column. It likely isn’t a necessity for most truck owners, but plenty of owners will likely find it advantageous.

Who It’s For: Drivers who want to tow, brag that they have class-leading towing capabilities, seek more premium aesthetics and finishes and value comfort while on the move. The latter attribute is aided by GM’s wise inclusion of an independent front suspension in lieu of a solid axle.

While you can definitely guide the 18-inch Michelin all-terrain tires (20s are a tick-box option) off the asphalt without much worry, thanks to the new lockable automatic four-wheel drive with low range, the Sierra HD isn’t a high-speed trail-thrasher like the Ford F-150 Raptor or obstacle basher like the Jeep Gladiator. It lacks things that off-road-centric competitors like the Ram Power Wagon offer, such as selectable locking diffs, disconnecting electronic sway bars and trail cameras.

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Watch Out For: The weakest spot on the Sierra HD is the interior. The cabin is a sedate and comfortable place to be, and it’s more upscale than the Silverado HD or the Ford Super Duty — but it feels dated, especially when compared to the Ram Power Wagon’s interior. Ram’s honking 12-inch touchscreen was a game-changer, and the Sierra’s equivalent control panel feels downright minuscule in comparison.

Granted, buyers likely care more about towing, power output numbers and that gratifying whoosh of 910 lb-ft from the 6.6-liter turbodiesel mill when they get on it, but if GMC is marketing top trims like the Denali as premium, the interior needs to go further to rise to that label.

Alternatives: You’ve got the Ram Power Wagon (starting at $53,350), but that doesn’t offer a diesel engine. (Ram engineers claim it was too much mass to suit off-road handling requirements.) Then there’s the Ford Super Duty (from $35,300) which does offer a 6.7-liter turbodiesel, as well as the Chevrolet Silverado HD (from $36,500), which can be fitted with the same 6.6-liter Duramax powerplant as the Sierra HD.

Review: Best-in-class numbers are things truck owners care about a ton, and the Sierra HDs clinch the top podium spots in a host of those areas. Both the 2500 and 3500 models are underpinned by a wholly-new, stronger, longer and taller ladder frame, utilizing beefier (yet lighter) materials. This, in concert with the upgraded powertrains, afford staggering maximum payload and towing capabilities. The Sierra HD can haul more than 3,500 pounds in the bed and tug more than 35,000 pounds. Indeed, GMC noted that all its one-ton duallys, regardless of spec or configuration, can tow more than 35,000 pounds — a claim neither Ford nor Ram can boast.

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A 6.6-liter V8 gasoline engine is offered in Sierra HDs, providing 401 horsepower (nine ponies shy of the Ram Power Wagon’s 410) and 464 lb-ft of yank (35 more than the Ram’s 429). The downside is that the engine is mated to a six-speed automatic; the Ram has two additional gears, while the Ford packs an extra four.

With a payload of 2,000 pounds of cut logs in the bed, our gas-powered Sierra 2500 HD AT4 crew cab struggled a mite to make it up some roads with a roughly-4-percent grade. On flat surfaces, however, the gas variant handled everything with aplomb — accelerating nicely, without braking issues or unnecessary body roll when cornering.

If you covet maximum twist, though, you’ll want the revised 6.6-liter turbodiesel Duramax V8. That sucker cranks out 445 horsepower and a monumental 910 lb-ft of torque — double the Power Wagon’s gas-powered engine. And you feel every last oomph of that grunt. Our Sierra 2500 HD Denali crew cab hustled even when laden with the same 2,000 pounds of lumber in the rear. We tugged a 12,000-pound box trailer behind a 2500 HD AT4 with surprising ease — even going uphill through the Wyoming mountains towards Idaho. Even with its slightly elevated ride height and more-forgiving, off-road suspension, the AT4 didn’t show any signs of strain. At a lunch break, we also got a short turn at towing the max trailering load, some 35,000 pounds; it was a laughably serene experience.

The new 10-speed Allison transmission helps the diesel HD find the right gear without much hunting, which provides more ride comfort. Indeed, the ride over some 60 miles was supple and even; other than needing to leave a little extra room for braking, there was no difference in the HD’s driving characteristics with a trailer hanging out back.

Hitching up a trailer is particularly simple, thanks to a motor mounted on the brake caliper that fires to mitigate any movement. A park hold assist helps reduce transmission strain, as well as sliding or shifting when you’re shifting into drive.

In a further bid to alleviate towing woes, GMC offers a class-exclusive ProGrade Trailering camera system, which pumps 15 different views from eight cameras into the infotainment screen. It’s designed so you can still see your load while cornering, and even comes with an (optional) internal camera so you can see how your cargo’s faring.

Perhaps the most innovative view was the Invisible Trailer, which stitches multiple feeds together in a single image to make the trailer seem to disappear. While it worked flawlessly in our 2500 Denali, it was a little laggy in the AT4 and went blank a few times, which we’ll chalk up to pre-production bugs for now. Overall, however, the camera set-up was a welcome tool.

A compact off-road loop in the diesel AT4 showed it’s handily capable of climbing piles of logs, provided you have a light foot. Give it the beans, and all that torque can result in a bit of wheel spin. It powered around banked piles of dirt and plowed through a sloppy mud-and-water feature with butt-wagging glee, firing admirable rooster tails of muck behind us.

Is it the truck you’ll want for serious off-roading? Perhaps not, but it can hang with the big dogs when it needs to. Small gravel off-road loops and gentle dirt trails in the diesel Denali HD showcased the suspension’s ability to sop up mild trail crud, though we’d have loved to flog it over something a bit more demanding to see how it handled it.

Verdict: GMC knows its clientele appreciate the supreme towing capabilities of its trucks, and the Sierra HD delivers on that promise in spades. If hauling or towing is part of your regular routine, the Sierra HD’s proficiency should send it to the top of your shopping list. And if GMC just elevated the interior a touch, it’d be almost impossible to look elsewhere.

2020 GMC Sierra HD: Key Specs

Powertrain: 6.6-liter turbodiesel V8, 10-speed automatic, two- or four-wheel-drive; 6.6-liter gasoline V8, six-speed automatic, two- or four-wheel-drive
Horsepower: Diesel: 445 hp; Gasoline: 401 hp
Torque: Diesel: 910 lb-ft; Gasoline: 464 lb-ft

GMC hosted us and provided this product for review.

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