What year/ model Bmw's will give me a 3.25 rear diff to swap onto my 86 325, is it a difficult process?, and will my cas milege suffer bad? I really dont want like 3,ooo rpms just to cruise at 75 mph. What will my revs be at normal highway speeds?? (around 70 75) I want to do this but im still a little weary about changing something this important. Will I really have a car that seems alot quicker? Thanks for all your help! All you guys are great!! Brian