Putting GMC's 2024 AT4X Trucks To The Test: Do Gas Or Diesel Engines Make Most Sense?

At an event dubbed "AT4Xpedition," GMC recently invited media to live out our collective Yellowstone dreams in the stunning picturesque mountains of Montana. The single drive program included five different trucks in AT4X and AEV Edition spec, with the hope being that a series of real-world on- and off-road adventures might clearly highlight the differences that alphanumeric nomenclature and options boxes can quickly and easily confuse on paper.

The 2024 GMC AT4X family compares similarly to Chevrolet's ZR2 and Bison trims, in this case applied to the mid-size Canyon and both the Light Duty (1500) and Heavy Duty (2500) variants of the full-size Sierra. For the first time, the AT4X trim expands to this Sierra generation while the AEV Edition adds even more of the off-road goodies that made the previous generation's Colorado and Canyon siblings such impressive four-wheelers. Like Colorado, however, the Canyon loses a diesel engine option. But like Silverado, the Sierra Light Duty now comes with a 3.0-liter Duramax turbodiesel standard, and the Heavy Duty gets an optional 6.6-liter Duramax V8.

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Now throw in skid plates, optional suspension packages, bumpers, and auxiliary electrical ports—confusing details that I tried my darnedest to keep straight throughout the course of a 14-hour day of driving through Montana.

I started off in a Canyon AT4X without the AEV add-ons. That means a three-inch lift versus the base truck, with Multimatic's sublime DSSV shock dampers, locking differentials front and rear, and "rocker protectors." Everything I learned ripping a Colorado ZR2 and Bison around the desert of the southwest carried over to the Canyon as we hustled along a winding dirt road headed west down the hill from Big Sky ski resort.

For a bit of fun, I even threw the truck into two-wheel-drive only with the rear diff locked to create some hoonigan-style drifts—but keeping up with the lead truck on off-cambered descending turns made 4-Auto a much wiser (and safer) choice. That spectacular chassis, featuring revised suspension mounting points, shines at top speed as washboards and smaller ruts simply disappear. And the choice to drop the shared diesel engine also helps to improve front-to-rear weight distribution through unavoidable slides. 

Of course, the new 2.7-liter inline-four's turbo lag and lack of paddle shifters, plus my hesitancy to turn traction control fully off, led to more than a few corners where I might have otherwise carried more speed out into straightaways.

Next I jumped into a Canyon AT4X equipped with the AEV Edition package, critically for a more serious session of rock crawling than the 2024 Chevrolet ZR2/Bison family drive in Johnson Valley included the month prior. The AEV kit includes another 1.5 inches of lift over the AT4X, steel bumpers, and hot-stamped boron steel skid plates, but the Multimatic hydraulic jounce control bumpers that come standard on the ZR2 Bison transition to optional on the GMC. Instead, the Canyon AT4X AEV Edition receives an auxiliary plug for accessories and lighting in the truck bed.

Whether rock crawling or ripping, all 12.2 inches of ground clearance and the standard 35-inch tires make the AEV Edition a serious step up for both capability and comfort. I truly tested those sliders, skidding along microwave and oven-sized boulders repeatedly while trying to avoid catching the rear diff on rocks and logs. We even blasted through a few mud pits, for good measure.

GMC and Chevy's shared development team made the decision to drop the Colorado and Canyon's diesel engine for this generation in the name of top-end power and weight, just as much as efficiency and simplicity. Now, the expanded diesel lineup on Silverado and Sierra makes all the more sense. The smaller 3.0-liter Duramax on a Sierra Light Duty puts out 305 horsepower and an impressive 495 lb-ft of torque, approximately none of which felt lost at well over 7,000 feet of elevation in Montana.

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Just check out the turbo in that engine bay, pumping even depleted oxygen levels into the engine to allow for ratings of 13,300 pounds while towing and a payload rated at 7,290 pounds. The shared GM-Ford 10-speed automatic's gear ratios no doubt helped, but even swapping between the 6.2-liter gasoline V8 and Duramax trucks, the Multimatics also contribute mightily to the sensation that these trucks somehow weigh less than stats on paper suggest.

Still, the 1500-class Silverado and Sierra chassis shared for this generation was not developed originally for a ZR2, Bison, AT4X, or AEV Edition. Sheer popularity demanded that GM introduce these trucks into the lineup regardless, but packaging 35-inch tires into the trucks simply didn't work out. Next time around, seems likely.

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The added weight of steel bumpers, skids, and even the optional Comeup winch push that 6.2-liter V8 to the edge of feeling a bit sluggish (altitude certainly doesn't help for a naturally aspirated engine). And perhaps that's exactly why the Sierra AT4X AEV Edition comes with the diesel standard, especially since buyers who truly plan to do any serious off-roading will likely throw on a set of 35-inch tires anyway.

On the other hand, the Heavy Duty Sierra AT4X with the Duramax and AEV Edition bolted on can creep up to a gargantuan curb weight of 8,605 pounds—weight savings likely explain why the 6.6-liter gasoline V8 comes standard on the larger truck. Part of that massive curb weight comes courtesy of a beefed-up Allison 10-speed, but both pump out gobs of power, if the gas leans towards higher-end output and the diesel just humps along with low-end grunt aplenty.

AEV's kit and 35-inch tires do keep the HD's tow rating down to "only" 18,400 pounds. The rest of the setup works well with the leafprung solid rear axle fitted with the AT4X e-locker, as well as the independent front suspension and torsion bars. No, at that kind of size and poundage, real rock crawling a la the Canyon portion of our day becomes impossible. But out on a few test loops around Expedition Overland's new ranch, the HD proved eminently capable for the kind of jobs that GM builds this kind of truck to perform flawlessly.

We navigated a few tighter bushes and boulders, to be fair, before blasting down and then up and then down again some steep, shale surfaces. Climbing in and out repeatedly to snap pics, I especially appreciated the electronically retracting running boards, but also got a chance to truly watch the suspension at work. Imagine a ranch excavator slides into a ditch—a Heavy Duty Sierra with the Off-Road drive mode, locking diffs, and 35s can get off the graded road, then all the torque in the world can haul that machinery back upright no problem.

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Of course, toy hauling fits into the picture, too. And there's a good chance that while towing a side-by-side on a trailer, the HD Sierra won't even notice (on-road or off). Only the reduced visibility of that enormous hood presents true challenges—after accepting the limitations of narrow trails or serious bouldering—but a suite of techy cameras help to compensate on all of the GMC trucks, regardless.

The kind of jobs and tasks that I imagine for the Sierra diesels definitely fit into GMC's longstanding "We are professional grade" slogan. And yet, no true mechanical upgrades versus the Chevrolet siblings differentiate the Canyon and Sierra from the Colorado and Silverado. Pricing does, though, so what gives?

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Instead of thicker axles or upgraded brakes that might make the difference between Light Duty and Heavy Duty trucks, GMC offers more luxury and more technology on its pickups than does Chevy. A unique Obsidian Rush interior adds white leather (questionable for a jobsite, to say the least) and 16-way power front seats include quite possibly the best massagers I've ever experienced in a car. Upgraded materials for touch surfaces also dot the trucks, as do AEV and AT4X badging right down to all-weather floor liners.

On the exterior, the Sierra's styling cleans up some of the more angular lines seen on the Silverado, with smoother side panels and a less aggressive nostril-style hood scoop. The Canyon and Colorado flip-flop there, however—I know, styling is entirely subjective. Sipping cocktails at the end of our day, as GMC and AEV unveiled a top-secret project still under wraps officially, I reached the conclusion that I'd take a Sierra over a Silverado, but still think the Colorado ZR2 Bison bests the Canyon AT4X AEV Edition.

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Pricing will come into play. The AEV Canyon and Bison Colorado remain mysteries, but an AT4X Canyon starts at around $55,000 plus delivery. Expect the AEV package to tack on another $8-10,000 so that this truck (and the Bison) slot in just below Ford's various Raptors.

Diesel Sierras ratchet up the sticker shock further, as the Light Duty AT4X starts at $79,200 before delivery and the AEV reaches $86,095 to start. The Heavy Duty, meanwhile, clocks in at $82,800 for the AT4X and a whopping $92,295 for the gas AEV Edition. But in Montana, luxury trucks blast around every bend of every highway, mostly maxed-out Rams (as on the Dutton Ranch) but also an impressive fleet of GMC pickups to explain the location choice for such a wide-ranging media drive. 

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Now with more beefy diesel engines to go with off-roading upgrades and the finest of modern creature comforts, expect GMC's latest AT4X and AEV lineup to attract even more of Montana's multigenerational legacy ranchers and city slickers alike.