Your milage sounds about right. I do a touch better with mine, but i have 3.42 gears in mine with narrow stock tires. And don't believe teh hype when somebody tells you you can do this tune or box and see 3-5MPG better. The lie o meter may read higher, but your actual milage won't go up that much. I've played with tuning ALOT, and have yet to find any magic combo that makes the milage jump way up. Drive it easy, and keep the RPM's down is about all you can do. When I'm trying for milage I will actually let off the throttle to let it shift then give it throttle again until I want it to shift again, then I let out and repeat. I try to keep my RPM's under 1800 at all times, even driving around town. The newer trucks with a VGT can see pretty big milage jumps from tuning since you can open the turbo veins up and reduce the load on the engine, but the LB7 was about as good as it could be in stock form.