18 MPG combined, that’s part of the deal for the 2020 GMC Sierra 4WD AT4 with the 5.3L V8. Buyers are drawn to the AT4 for its rugged styling, off-road enhancements, and the commanding presence it offers. Fuel efficiency is a secondary concern, far behind capability and image. This truck is bought by those who need or strongly desire its specific skill set, and they understand (or accept) the fuel costs involved.

City and highway performance

The EPA estimates 16 MPG in the city and 21 MPG on the highway. The city MPG reflects the reality of stop-and-go traffic, where the Sierra’s weight and V8 engine demand more fuel to get moving. The highway figure, while still modest, demonstrates the benefit of the 10-speed automatic transmission, which allows the engine to settle into a more efficient RPM range at cruising speeds. These numbers reflect the inherent compromises in a full-size, off-road-oriented pickup.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2020 GMC Sierra 4WD AT4 5.3L at $2,450. This figure is based on driving 15,000 miles per year and using the national average fuel price at the time of calculation. Keep in mind that your actual fuel costs can vary significantly based on your driving habits, local fuel prices, and the grade of gasoline you choose. The EPA assumes regular unleaded, but some drivers may opt for premium in the belief it improves performance, further increasing the annual expense.

Real-world expectations

While the EPA estimates provide a baseline, achieving those numbers consistently in real-world driving can be challenging. Expect lower MPG if you frequently tow trailers, haul heavy loads, or spend a significant amount of time off-road. Aggressive driving, including rapid acceleration and hard braking, will also negatively impact fuel economy. Conversely, gentle acceleration, anticipating traffic flow, and maintaining a consistent speed on the highway can help you get closer to the EPA estimates, if not exceeding them on occasion. Examining SIERRA MPG across all years, the 2020 AT4 5.3L is very similar to other model years, and very consistent compared to the rest of the Sierra lineup.

How it compares

Compared to its competitors, the Sierra AT4’s fuel economy falls within the expected range for a V8-powered, four-wheel-drive pickup with off-road aspirations. A similarly equipped Ford F-150 with the 5.0L V8 achieves roughly the same fuel economy (around 17 MPG combined in 4×4 configuration). The Toyota Tundra, known for its reliability but less so for its efficiency, typically delivers lower numbers (around 14-15 MPG combined with its 5.7L V8). The Chevrolet Silverado, being mechanically similar to the Sierra, offers comparable fuel economy, though subtle differences in tuning or aerodynamics might result in minor variations. A RAM 1500 with the 5.7L Hemi V8 and eTorque mild-hybrid system might offer a slight edge in fuel economy, potentially reaching 19 MPG combined, but that’s the exception, not the rule. For those truly concerned, reviewing all Gmc fuel economy data is highly advisable before committing to the AT4.

Tips to maximize efficiency

Avoid aggressive acceleration. The 5.3L V8 has plenty of power on tap, but flooring the accelerator pedal will quickly drain the fuel tank. Gentle acceleration, allowing the transmission to shift smoothly, can significantly improve fuel economy, especially in city driving.

Maintain proper tire inflation. Underinflated tires increase rolling resistance, which reduces fuel efficiency. Check your tires regularly and inflate them to the recommended pressure listed on the doorjamb sticker. This is particularly important if you frequently air down your tires for off-road use.

Minimize idling. Letting the engine idle for extended periods consumes fuel without covering any distance. If you’re stopped for more than a minute, consider turning off the engine, especially during cold weather when prolonged idling is often used to warm the cabin.

Reduce aerodynamic drag. Removing unnecessary cargo from the bed and ensuring the tonneau cover (if equipped) is properly closed can improve aerodynamics, especially on the highway. Consider removing roof racks or other accessories that create wind resistance when they are not needed.

Use cruise control wisely. On relatively flat roads, using cruise control can help maintain a consistent speed and optimize fuel economy. However, avoid using cruise control in hilly terrain, as the transmission may downshift frequently to maintain speed, negating any potential fuel savings.