It's been six months since we first wrote about the work truck that we're driving. As promised, we have our first update now that we've driven it 7,000 miles. As a reminder, the four-wheel-drive GMC is equipped with the 445-horsepower, 6.6-liter turbo-diesel V-8 Duramax engine mated to the six-speed automatic Allison transmission.
The full-size crew-cab pickup truck has plenty of amenities and doesn't lack any creature comforts. The cab is spacious with plenty of room to fit six average-sized adults comfortably. The infotainment system is easy to use and didn't take long to get adjusted to. Being the lowest-rated heavy hauler of the big-three one-ton pickups, we were surprised at how competent the heavy-duty GMC Sierra 3500 was when towing heavy loads. Although the GMC's driver information display does not show what gear the truck is using, it does provide all the other information needed to monitor the status of the truck's systems.
We've spent a lot of seat time in this truck and it's comfortable on the long haul. It's easy to adjust the seats and the steering wheel controls put everything within reach. Voice-activated commands make navigating the system simple.
Towing a heavy trailer for eight hours straight is not nearly as stressful as one would expect. The massive size and heavy weight of the truck help keep it composed while towing at its rated limit: 17,000 pounds for this single-rear-wheel model. There is always plenty of power to get the truck and trailer up any grade, and the exhaust brake does an excellent job of keeping the speed where it should be on steep downgrades. Now that the transmission has learned our driving habits, the hard shifts we initially reported have smoothed out significantly.
The only time the truck had issues was on extremely steep slopes with low speeds and hairpin turns. Basically, when the truck is in 1st gear, the torque converter doesn't seem to lock up. This limits engine braking on downgrades, which puts more stress on the brakes. Not locking up the torque converter also causes the transmission temperature to climb on steep uphill grades. When pulling a 17,000-pound trailer up a mountain with grades reaching 20 percent, the dash displayed a notice that the transmission was overheating and we needed to pull over to let it cool down.
We found the truck had enough power to get into a higher gear, which would lock the torque converter, but the lower speed limit and hairpin turns didn't allow it. Going down the other side of the hill, the mountain had similar grades and low speed limits, which caused the brakes to heat up and fade just a little.
As for fuel economy, when driving without a trailer in tow, we average more than 20 mpg combined, but overall, the Sierra is in the 15-mpg range according to its computer. As we rarely drive it without a trailer attached to it, low fuel economy is expected.
In our first story about the GMC Sierra 3500, we mentioned that there was a little glare coming off the hood scoop. This problem isn't common, and while it doesn't show up well on camera it can be distracting when light hits the hood scoop just right.
First Maintenance Visit
With less than 3,000 miles, we noticed the rear tires were wearing away. The fronts looked nearly new, but the rears were almost down to 50 percent tread. The incredible power this truck puts down can wear out tires quickly, especially when towing heavy loads.
We also thought we noticed some lean: When standing behind the truck, it is clear the driver's side is lower than the passenger's side. We took measurements and found there was a difference of more than an inch. We followed that up by weighing the truck with a scale under each wheel. The driver-side front wheel had 55 pounds less weight on it than the passenger-side front. The opposite was true for the rear of the truck, with the passenger-side rear weighing in 110 pounds less than the driver-side rear. The lean isn't noticeable when driving the truck, but it had us concerned.
The other issue we encountered started within the first month of driving the truck: The low coolant light would come on periodically and then go away. Once we had broken in the engine a bit and started towing heavy loads, we noticed the smell of antifreeze when we parked the truck in the garage. Upon further inspection we found that one of the coolant hoses had separated from a connection. The hose was reconnected and there have been no problems since.
So, we took the GMC Sierra 3500 in for an oil change and checkup at 3,200 miles. The truck's computer readout claimed an oil life of just less than 50 percent at that point. Since we had worked the GMC Sierra hard and this was its first oil change, we played it safe and took it to the dealer. We asked the dealer to also rotate the tires front to rear, check for coolant problems and any chassis problems that might cause the truck to lean. No issues were detected and the truck was given a clean bill of health. GMC gave us two free service visits when we purchased the truck, so this first one was on them.
One of the few issues with this truck is filling the diesel exhaust fluid tank. When filling at truck stops, the truck needs to be positioned precisely to allow the DEF hose, located on the driver-side pump, to reach the DEF tank fill point, which is located on the passenger side of the truck.
Filling the tank with the 2.5-gallon jugs is also an issue. It's hard to get the jug in the proper location because of the limited amount of space between the engine and the hood. The truck is also quite high, which can make it difficult for some people to hold the 20-pound DEF jug high enough to fill the tank.
After six months, the 2017 GMC Sierra 3500 has really grown on us. It's comfortable for a one-ton truck, it tows exceptionally well and has an incredible amount of power. The GMC Sierra 3500 is always chosen over the medium-duty work trucks in our fleet for towing heavy loads. The crew-cab long bed makes it difficult to park the pickup in smaller parking stalls, but all that space for hauling people, gear or materials makes the inconvenience worth dealing with. Overall, this GMC Sierra 3500 has given us an excellent experience so far. More updates to come.
Cars.com photos by Matthew Barnes