Guidane needed on reverting a modded Mk IV to stock

[finaltable]

Thanks. In the back of my mind I thought electronics mods would be a bad thing to try and undo. My concern about power is primarily related to efficiency. Generally, more power = less mpg, and while I am not looking for a Prius, I have to make a trip that is about 250 miles round trip every other week and would prefer to get better than single digit mpg doing it. I make the trip now in a Chevy truck and can at least make the round trip on one tank of gas.

In the area of exhaust, I am willing to bet that if I found a car with aftermarket exhaust I could probably find someone willing to trade their stock exhaust to me straight up.