Unit and Sky are right. Gears will increase your top end, believe it or not. I have had my car upwards of 140 mph since the gear swap. Before it was struggling to get to 130mph. They will eat up a little more fuel if you do mostly highway driving, but through town they won't make any difference because you will more than likely drive in a higher gear. Mine gets close to the same gas mileage it did before and it sees between 50 and 70 miles of highway driving a day.
You're looking at about the same price for a full exhaust which most people can install themselves, versus a set of gears, traction-lock rebuild kit, and assembly kit plus labor. Gears are going to make the biggest difference though. I would suggest that if you do the gears make sure you rebuild the traction-lock while you're in there.
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