Tip - How to Improve Gas Mileage on a V8 Sierra | eHow

According to fueleconomy.gov, the GMC Sierra with a V8 gets roughly 12 miles per gallon in the city and 18 on the highway. GMC has five models of the Sierra: 1500, 2500HD, 3500HD, Denali, and Hybrid. The Hybrid V8 gets 21 miles per gallon in the city and 22 on the highways.The Sierra is a large truck with a powerful engine, but you can improve its...