ive just converted my car to m6. i have slp headers redy to go on and my speedo is way off. the trans came out of a car w/ 4.10s mine are 3.23. i need to program my computer what is the best system?lt1 edit tunercats or is there some others that im not aware of. i dont want a mail order because thats only good for now and after other mods such as gears i will be in the same place. oh yeah if my reverse lights dont work and its wired up right the only thing it could be is the switch on the side of the trans right?