What should I get, 3.55 or 3.73 gears? Primary concerns with the 3.73's are gas mileage and what kind of RPM's will I be pulling at 75mph if I have 17 inch rims? I already know how quick the 3.73's get up there, my buddy has them, but I was curious if this is going to be a toll on my engine and if it is going to effect my gas mileage SIGNIFICANTLY.