The easiest and cheapest way to change your final drive ratio is to change your rear tires to the smallest diameter tires you can find. 285/30 or 295/30 depending on the exact tire should reduce your final drive ratio by about 5%. It's not a huge change, but you don't have to drop your engine and break open your gearbox. The Continental ContiSportContact 2 is even available in a 255/30 that reduces the final drive ratio by 9%. It's a crappy tire, though.