17 MPG combined is the stark reality for owners of the 2020 GMC Sierra 4WD AT4 with the 6.2L V8. Nobody buys this specific configuration of the Sierra expecting Prius-like fuel consumption. They buy it for its commanding presence, its off-road capability thanks to the factory-installed lift and Rancho shocks, and the strong power delivery of that iconic V8. This is a truck for those who prioritize capability and attitude over efficiency, and are willing to pay the price at the pump.

City and highway performance

The EPA estimates the 2020 GMC Sierra AT4 6.2L at 15 MPG in the city and 19 MPG on the highway. These numbers reflect the challenges of moving a heavy, four-wheel-drive vehicle through stop-and-go traffic, and the aerodynamic limitations of a lifted truck at higher speeds. The 10-speed automatic transmission does its best to keep the engine in its optimal power band, but ultimately, physics and the engine’s displacement dictate the fuel consumption. The highway figure is somewhat respectable given the truck’s profile, but it’s still a far cry from the efficiency offered by smaller trucks or even some full-size trucks with smaller engines.

Annual Fuel Cost

According to the EPA, the estimated annual fuel cost for the 2020 GMC Sierra 4WD AT4 6.2L is $3,400. This figure is based on driving 15,000 miles per year and using national average fuel prices. Keep in mind that your actual fuel costs may vary depending on your driving habits, the type of fuel you use, and regional fuel prices. If you do a lot of heavy towing, off-roading, or spend most of your time in city traffic, expect to easily exceed this already hefty annual fuel bill. It’s a significant expense to factor in when considering owning this particular truck.

Real-World Expectations

While the EPA estimates provide a baseline, real-world fuel economy for the 2020 GMC Sierra AT4 6.2L often falls short. Many owners report averaging closer to 13-16 MPG in mixed driving conditions. Factors such as aggressive driving, aftermarket modifications (larger tires, roof racks), and frequent towing can all significantly impact fuel consumption. A heavy foot on the accelerator is particularly punishing with this engine, as is consistently using four-wheel-drive on paved roads. Expect to see the best numbers on long highway drives with a light load and a consistent speed within the posted limit, anything else will drop below the already low EPA estimates.

How it compares

The 2020 GMC Sierra AT4 6.2L isn’t exactly a leader when it comes to fuel efficiency in the full-size truck segment. The Ford F-150 with the 2.7L EcoBoost engine achieves a combined 20 MPG on 4×4 models. Even the Ram 1500 with the eTorque mild-hybrid V8 sometimes nets a combined MPG in the low 20s. Of course, these configurations offer different performance characteristics, and the AT4 boasts off-road specific hardware, but the fuel economy difference is undeniable. If fuel economy is a primary concern, other full-size trucks, even those with V8 engines, can offer significantly better mileage. If you’re curious, you can browse all Gmc fuel economy data to see how other GMC models stack up. You should also look at SIERRA MPG across all years to understand the range of fuel economy figures for this model.

Tips to Maximize Efficiency

Given the nature of the 6.2L V8 and the AT4’s off-road focus, extracting maximum fuel efficiency requires a conscious effort. Avoid aggressive acceleration and braking, as these actions dramatically increase fuel consumption in a large-displacement engine. Gentle and gradual transitions will yield noticeable improvements over time.

Ensure your tires are properly inflated to the recommended pressure. Underinflated tires increase rolling resistance, forcing the engine to work harder and burn more fuel. Check your tire pressure regularly, especially during temperature changes, as this can affect inflation levels.

Minimize idling. Leaving the engine running while stationary consumes fuel unnecessarily. If you anticipate being stopped for more than a minute, turn off the engine. Modern vehicles are designed to restart quickly and efficiently, making idling a wasteful habit.

Reduce unnecessary weight. Hauling around extra cargo in the bed of the truck decreases fuel economy. Remove any items that are not essential, as every pound contributes to increased fuel consumption. Consider removing the tailgate if you have bed cover and aren’t hauling any material that could fall out, since the tailgate is designed for aerodynamics when left up.

Use cruise control on the highway whenever possible. Maintaining a consistent speed helps prevent unnecessary acceleration and deceleration, optimizing fuel efficiency. Set the cruise only in the correct towing mode. Remember though, cruise control is best used on flat terrains to avoid sudden down-shifting on inclines that can burn extra fuel.