Looking at gears and a stall converter. I have an A4 99 trans am and currently has 3.23 gears. How much of a difference would 3.42's make. Or would 3.73 be better even though the car is a Daily driver. And how would a 2500ish stall work with a full bolt on car?

 

3.73s will be better, unless you're using it as a highway cruiser for the most part, then they might be annoying. 2500 stall will work well, although I expect most of the stalled guys will probably suggest a little higher. IMO a one step up gear change won't give you much of a sotp difference.