I recently aquired a 2006 silverado 1500 4x4 with the 5.3. Curently I get 16.5 to 17.5 mpg. I also have a k&N air filter in it. I have been considering three lift options, while keeping the stock tire size. 1. leveling kit. 2. 2" lift kit. 3. 2" lift and leveling kit. I was wondering what kind of effect the lift would have on my gas mileage. I have a friend who has a toyota tundra, he put just a leveling kit on his truck and the gas mileage dropped down 3 - 4 miles per gallon.