Dallas Mustang sells a little box called a SpeedCal. I just ordered one. It can be tuned for your gear, and tire size and will simply plug into your speed sensor. Best of all, if have two sets of wheels, you can keep changing it as needed. It is alot cheaper than a chip at only $99. I'll let you know how it works out when I get it in.chipcecil said:I am changing for 3.23 to 3.73 in a 2001 GT automatic, how do I set the speedometer?