im after making my car rev less when in fith on the motor way as its thirsty to say the least. my problem is what do i need to resolve my problem. my car is an import 94 sti v1 with a 4.1 final drive. so ive been told. can i swap final drive and rear diff easily

 

I would suggest a call to the box expert, David at Welcome to the API website
He might suggest changing 5th for a UK 5th gear which is much longer than your current 5th.
Far cheaper option, far quicker to do, far better economy!

Call David, tell him '911' sent you.