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2020 GMC Sierra 3500 HD Denali Duramax: Tested on the Road and Trail

Yes, you know we rockcrawled the dualie.

The 2020 GMC Sierra 3500 HD Dualie boasted 6.6 liters of Duramax diesel power and two more tires in its rearend than usual in our test. See how this dualie fared on- and off-road in the 2020 Pickup Truck of the Year test.


What's Hot

  • More than 30,000 pounds of towing capacity
  • Downright surprising off-road chops
  • 6L Duramax and 10-speed transmission make for a stellar combo

What's Not

  • High-class interior could use a redesign

What's New For The 2020 GMC Sierra Denali 3500 HD?

The GMC Sierra 3500 HD Denali is a land-dwelling tugboat moonlighting as an off-roader with a payload of 5,607 pounds and the ability to pull north of 30,000 when equipped with a gooseneck. Our tester came with the familiar LP5 Duramax powerhouse, good for 445 horses and 910 ft-lbs of torque, and bolted to a freshly revamped and Allison-badged 10L1000 10-speed automatic transmission. Engineers tackled issues of heat generation and power loss in the transmission by bypassing the torque converter and, when Tow/Haul mode is selected, locking the trans in First gear to get every foot-pound of the truck's torque to the ground in demanding towing situations. Power is then routed through the MP3025 transfer case and its Autotrac system, an "industry first" for the heavy-duty segment. Brawnier driveshafts move the power into the rear differential and its gargantuan 12-inch ring gear before the dual rear wheels deliver it to the ground.

Did We Flex the Dualie?

With an extra pair of tires on the rearend, the 8,355-pound GMC Sierra 3500 HD Denali made its way up the 22-degree RTI ramp earning it a score of 334.

How Fast Does It Go?

The 6.6L turbodiesel got its 445 ponies and 910 lb-ft of torque to the ground, making the dualie the third-fastest truck of the lineup with a 0-60 time of 7.3 seconds. We covered the quarter mile in 15.7 seconds and hit 89 mph in the process. After mashing the brakes, we got the rig back down to a stop in 136.6 feet.

Inside and Outside the GMC Sierra 3500 HD Denali

"Only way it could look better is with my fifth-wheel behind it!" said a judge while examining the Sierra 3500 HD Denali before testing began. Some judges nitpicked the exterior, asking for "a little less chrome," while one judge wrote "more exterior lights than my girlfriend puts up for Christmas!" We were fans of the CarbonPro bed and how the truck came ready to accept a gooseneck and/or fifth-wheel towing setup. Also favored by the judges was the six-function MultiPro tailgate, the 12 corner tiedowns, and 120-volt power; all in the "thank God it's a long" bed. We also witnessed judges poking around the grille and hood scoop, uttering phrases like "this hood looks trick," and "I'm glad the scoop is functional."

GMC dressed the Sierra 3500 HD's interior in Walnut and Dark Ash Grey hues with bits of open-pore wood trim, meant to remind us of hand-planed furniture. Although we cringed at the thought of soiling the immaculate upholstery, many were otherwise content spending time in the rig's cabin, penning comments like "it's roomy and warm" and "reminds me of some squire's study—it needs a fireplace and I need a monocle." We were fans of the head-up display and the layout of digital gauges, though some judges noted their wishes for a bit of help stepping up and into the Sierra 3500.

Highway Performance

From the initial pulls while testing acceleration and braking to the final all-day push back to civilization on the interstate, judges were constantly in awe of the Sierra 3500 HD's comfort. "Sure rides smooth for a truck with 75 psi in all six tires," is how one judge described their experience after a lengthy pavement session. Steering and braking were "better than expected," considering the size and one judge wrote, "it drives straight like a missile," while another said, "definitely not plush but planted and stable."

Power from the 6.6L Duramax mixed with the imperceptible shifts through the Allison's 10 cogs inspired comments such as "pulls like a freight train" and "the power band is right where I want it." Peering over the hood reminded us of the blindspot lying in front of the grille, however, with a peek at the forward-facing camera, fears of bumping into hidden objects out front melted away. After a week on the roads and trails, we found that the dualie logged a combined fuel economy of 14.4, not too shabby for a 1-ton.

Off-Road with the GMC Sierra 3500 HD Denali

Anyone with questions of "how will the dualie do off-road?" got an answer in a big way. "She's a bit wide in the hips," wrote a judge after maneuvering the 1-ton truck through a craggy canyon and over a jagged ledge climb, but with that said, the Sierra 3500 HD went everywhere its single rear-wheel compatriots went, with some extra attention to the width of the extra wheels. While its 172-inch wheelbase, lack of complete skidplate coverage, and all-season tires did little to help the truck off-road, judges noted that having two extra wheels on the ground seemed to help push the truck along when going got rough, albeit after massaging the throttle to engage the "often-more-than-fashionably-late-to-the-party G80 mechanical locker" in the rear differential. In the sand, we gave the dualie higher marks on ride and comfort than some of its competitors with dedicated off-road packages. "Sliced isn't the word, steamrolled, perhaps?" is how one judge described the 3500's performance in the dunes. When ascending a gravel two-track with a slathering of slush, snow, and mud, the truck climbed appreciably well before we even needed four-wheel drive. However, the slippery surfaces brought to light the limitations of traction control. Traversing rolling dips and sharper drop-offs was "deceptively smooth" and "far better than expected" while washboards were the "Achilles' heel" of the Sierra 3500.

Our Take

If your definition of work or play involves 15 tons on the gooseneck and a rutted forest road, the Sierra 3500 HD Denali is your well-dressed workhorse with four-wheel-drive chops in its back pocket.