I started out with 1.5-2" of suspension lift. Mine is now at around 2.5" of suspension lift, still no body lift. Even after changing diff gears, the mileage still suffers from larger tires. The aggressive tread itself actually has a small effect on mpg, too. The additional rotating mass of larger tires makes it have to work harder to accelerate, so you'll use more gas that way. At highway speeds, aerodynamics are worse due to such a large area of the front view of the tires being exposed directly to the oncoming air. That's partly due to larger tires and a lot due to an off-road bumper that's designed to give more clearance at the outsides of the bumper. The stock bumper tried to go as low as would still look good to push air away from the front of the tires.