The fuel tank capacity of a GMC Envoy XL 6-cylinder is approximately 25 gallons. Coupled with the average fuel economy of 17 miles per gallon, the GMC Envoy XL manages to achieve approximately 425 miles per full tank.
The Envoy is a full-sized sport utility vehicle that can tow just over 6,000 pounds when equipped with a proper tow bar. However, due to its large size and 2-ton gross weight, the four-speed automatic transmission generally fails to keep the engine's RPM low. This results in an average fuel economy of under 18 miles per gallon. To improve the gas mileage of the SUV, install tires that offer better traction performance or look for ways to reduce the weight of the chassis.