I got a 4.8 and wow what a difference. Its only been two weeks since I got mine and now I gotta race from a little roll or ill spin them tires real bad all through first. Get it man. You won't be disappointed!!!! Sorry allen but haha your gas mileage gain is a myth ....at least for me I can't keep keep my foot out of the throttle with my tuned bolt on 4.8 ECSB. I beat 5.3 chevys now haha. Trust me you won't regret it