kicking around an idea

There is a possibility that putting in taller gears could help your time, but on launch or shifts you might bog down and get below the power band. I don't doubt that they exist but I've never seen gears for the Ford 8.8 that are that high. As far as mileage goes, I don't know how much improvement you would see. I have 3.55s in my car and I don't really turn that many revs in 5th at 70. You would have to go pretty fast to keep from lugging the crap out of it on the highway. I could be wrong, might be worth a shot.