You can't use a Tuner on a 97 GT to fix it. You either need the correct speedo gear or a speed cal.
Of course you need to figger out what gears you have first.
Mike
The Multi-Function switch(on steering column) is most likely your problem. The contacts in them corrode easily over time. If your fairly mechanical you can take it apart and clean the contacts, and put a little die-eletric grease on them. I have repaired a couple this way before. Or you can just...
Speedcal from Dallas Mustang is the way to go. I swapped the speedo gear at first, and it just got chewed up in about 200 miles of use. It was a 23 tooth gear (white) from John's Mustang Late Model Mustang 5 SPEED SPEEDO GEARS .
Mike
I have PI intake & Cams (NPI heads) running 3.73 gears and tunes tweaked by LaSota Racing.
I have no problems running with 99-04 stangs.
http://img.photobucket.com/albums/v477/sfcmac1/AUTOBAHNhere.jpg
I got mine from LaSota Racing. Came with 3 tunes, and for 90 days free support tweeking the tunes you datalog. The guy there is Don and his turn around time on every datalog I sent him was the same day. Great service.
Mike
On the Cheap for me was: PI Intake & PI Cams, K&N filter, 3.73 gears, Xcal2 with tuning support from LaSota Racing.:nice:
Car runs like a Raped Ape now!!!:nice: Of course I was able to do the installs myself, except the gears.
Mike