Editor’s Note: This GMC AT4 Sierra article was originally published in Overland Journal’s Summer 2023 Issue.
For our first full-size project vehicle, we selected a half-ton GMC with their AT4 (all-terrain 4WD) package. The base Sierra is known for its quality of assembly, overall driver comfort, and 60,000-mile, bumper-to-bumper warranty. In recent years, GM has been taking overlanding by storm, releasing model after model well-suited to this form of travel. It started with the ZR2 Bison and now includes multiple AT4 models, the new AT4x Sierra and Canyon, and the much-anticipated AEV variants.
Ideally, we wanted an extended-cab, standard-bed Sierra, but it was not available in the AT4, so we chose the crew-cab, standard-bed option, which gives a 6.5-foot bed length and a 157-inch wheelbase. It’s a big truck with an overall length of just over 20 feet, so the extra clearance of the AT4 lift was necessary. The package comes with 32-inch Goodyear Duratrac tires on 18-inch wheels, Rancho shocks, additional skid plates, and the G80 rear locker.
The drivetrain we chose is the impressive 3.0-liter Duramax diesel mated to a 10-speed automatic. Not surprisingly, this is my favorite attribute of the truck and is the best overall engine/transmission combination of any vehicle I have ever owned. It produces 460 pound-feet of torque and 277 horsepower, achieving 0-60 mph in less than seven seconds, with a towing capacity of 9,000 pounds. The most impressive specification is the fuel economy, a seemingly impossible 23 mpg during mixed driving in its current configuration. Even with the camper attached, it achieves 18 mpg.
In stock form, I was admittedly surprised by the trail performance of the AT4, the Duratrac tires and the additional clearance helping the GMC negotiate our test course. My primary criticism is with the G80 rear locker, which would be a reasonable solution 25 years ago, prior to advanced traction-control systems, but in 2023, it is a liability. The nature of the locker requires wheelspin to engage, which translates to there being no usable traction control of the front tires. It also results in unnecessary damage to the trail and the high likelihood of the truck sliding off line once the locker suddenly engages. Again, it is better than open diffs, but a “Trail Mode” traction control would be a more suitable option for the AT4 model. Fortunately, the AT4x solves all of this with both rear and front lockers and multi-mode traction control.
Stage One
For Stage One of the build, we kept the suspension stock and installed a set of 17-inch AEV Crestone beadlock wheels. The 17-inch wheel just fits over the calipers but provides an improvement in flotation and carcass section height. For the first set of tires, we installed BFGoodrich 295/70 R17 All-Terrains. They fit the vehicle with limited rubbing and measured just over 33 inches.
For overlanding, we wanted to install a bed rack and chose the Putco Venture Tec rack, as it was full length (for the 6.5- foot bed) and height, allowing for the installation of an IKamp-er hard-shell roof tent. To the sides, we mounted a set of MaxTrax and kept the bed open for camping gear and supplies. On the inside of the GMC, modifications were kept to a minimum, but we did install the whole gamut of Tuffy security boxes, including the center console lock box and the rear under-seat, full-length storage locker. The center console unit is particularly clever, retaining quick access space on top of the lockable section. This is a great place to securely store a GPS, weapon, cash, and documents. In the rear storage, I keep tools, an OBDII scanner, a drawbar, and basic recovery gear. This keeps these items safe from thieves and secure in the event of an accident or rollover. The Tuffy boxes are one of my favorite modifications to the AT4.
For navigation and communication, we selected the Garmin Overlander GPS and the InReach Mini. It is important to have reliable communications in the backcountry, so we combined the InReach with a WeBoost cell booster, a multi-band handheld HAM radio, a set of Midland GMRS handhelds, and even a Starlink RV unit. This allows us to camp remotely with confidence and explore for longer periods as we can get work done in the backcountry.
The Stage One configuration is well-suited to the payload and capabilities of the Sierra 1500, and we kept it in that mode for the lion’s share of the mileage. It allowed us to use the truck as a truck, hauling motorcycles and going to Lowe’s (they give the best veteran discount).
Stage Two
For Stage Two, we wanted to optimize the Sierra for remote travel and work from the field, which meant extended periods of living in the truck while exploring and working. If there is one thing I have learned, it is that months living out of the vehicle is best complemented with a way to escape the weather and a way to comfortably poop in said weather. I am happy living out of a bivy sack on a motorcycle for months, but if I have a full-size truck, I am going to make use of the space and payload. For that, we purchased a Scout Kenai 9.5-foot camper.
Deciding which camper to purchase was quite the exercise, but I had a few requirements. The most critical was weight, as I was dealing with a 1,500-pound payload and only a few options for improving the number (primarily removing the tailgate and rear seats). With the right modifications, I knew the truck suspension could be tuned to support the load, but GVWR is a fixed number despite the springs or jounces one installs. As a result, I needed the camper to weigh less than 1,200 pounds, and there were only a few options available that still had good insulation and the ability to fit a toilet and shower. I do like pop-top campers, but I felt there was no real incentive to justify the compromises of a pop-top in this case. This left me choosing the Scout Kenai, which combines light weight, durability for rough roads, and four-season capability. What put me over the edge was the Dickinson fireplace/heater (no longer offered), which makes the camper about as cozy as a mountain cabin.
The Scout has several important attributes, starting with the 1,080-pound dry weight. With the camper jacks removed and a few other items (like the bed extension pads and support) pulled out, it met my weight requirements. The camper is constructed from reinforced, multi-layer composite panels, all supported by aluminum extrusions that protect the corners. There is no plumbing (save for a 7-inch sink drain hose) and no 120-volt wiring. The cabinetry is constructed from durable plywood, finished in a handsome dark gray. There are no drawers or doors, resulting in nothing to fail. I used simple soft-sided organizers from Dometic and Red Oxx to manage everything. For 12- and 120-volt power, I use a Goal Zero Yeti 1500x lithium power station, which includes everything from USB-C to 12 volt to a 120-volt inverter to a solar charge controller. The Scout has a 180-watt solar panel on the nose cone, which has met all the modest means of the camper. The Goal Zero does have an optional 50-amp charger to run off of the truck’s 7-pin, but it did fail after about six months of use.
After nearly two years, the Scout has exceeded my expectations and certainly justified the purchase price. I like its simplicity and robustness, even with thousands of miles of dirt-road travel. The composite sides hold up well to brush and limb contact from the trail, with only the windows showing noticeable scratches. I suggested a few changes to Scout, and they were implemented with the V2 camper, including an improved dinette layout and windows in the sleeping area. The exhaust fan needs to be larger for the Kenai model, but otherwise, I was a happy camper. I made a few modifications to the Kenai, including fitting a Nature’s Head composting toilet and a Dometic CFX55 fridge.
My final modifications for Stage Two were to improve the suspension damping and load management. For that, we worked with Eibach on their new Pro-Truck coilovers and rear shocks. The coilover has increased spring rate and improved rebound control, and the rear shocks helped to better manage the Scout’s weight. The coilovers with a small bucket spacer provided an extra inch of ride height in the front. I used a Hellwig Silent Support helper spring set in the rear to reduce sag (it reports up to a 2,500-pound load capacity, but GVWR should never be surpassed). To manage jounce, I installed one of my favorite modifications to any vehicle (even stock), the Timbren SAS progressive bump stops. This entire system has worked in concert to support and control the weight of the camper. I also installed a set of Kenda Klever 35×10.5 R17 tires on the AEV wheels, which provided an additional inch of ground clearance for more technical terrain. It is such a perfect size, but they did require a bit of “adjustment” to the wheel wells for them to fit without rubbing. These tires rounded out the capability needs of the AT4.
GMC AT4 Sierra 1500 Duramax: Conclusions
Over the past two years, I have driven the AT4 29,000 miles, usually loaded with the camper, which I spent two months living out of. Most days, I was off-highway, exploring an area or finding a campsite. During that time, we did not have a single warranty claim and have experienced no failures in the truck or camper. The AT4 was safe and comfortable to drive for significant distances, providing radar cruise control and a head-up display to keep the driver’s attention on the road ahead. We drove from the border of Mexico to nearly the border of Canada twice and as far east as Dallas. It hauled motorcycles and was pushed within 700 pounds of GCVWR while hauling a sailboat from Texas back to Arizona. Incredibly, we traversed a section of Hell’s Revenge in Moab with the camper attached. It took me everywhere I wanted to go, sipped fuel, and rewarded me with a fireplace and stunning view at the end of a long, dusty day.
Even 10 years ago, the thought of remote travel using a full-size truck was often frowned upon, the naysayer espousing the limitations of big trucks in technical terrain, the lack of aftermarket support, or their suitability for international travel. In reality, the full-size revolution is here to stay, and I am a naysayer turned believer as our two-year GMC AT4 Sierra project comes to a close.
Resources
AEV Wheels: aev-conversions.com
BFGoodrich Tires: bfgoodrichtires.com
Dometic: dometic.com
Eibach Suspension: eibach.com/us
Garmin: garmin.com
GMC Trucks: gmc.com
Goal Zero: goalzero.com
IKamper Roof Tents: ikamper.com
Hellwig Overload Springs: hellwigproducts.com
Kenda Tires: kendatire.com
MaxTrax: maxtraxus.com
Midland: midlandusa.com
Nature’s Head: natureshead.net
Putco Racks: putco.com
Red Oxx: redoxx.com
Scout Camper: scoutcampers.com
Starlink: starlink.com
Timbren Bump Stops: timbren.com
Tuffy Storage Boxes: tuffyproducts.com
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