there is a converter tool available for around $150 that goes in line with the vss harness.
I am in the same boat. PO switched from 3.08 to 3.73 and when I am running 70 according to gps, my speedo reads 80.
funny thing is its accurate at 35. the faster I go the more its off.
I would have thought the inaccuracy would be linear not progressive.

 

this is all you need
Speedometer Recalibration Gears for 1979 thru 1998 Ford Mustang

this is the one you need
392-STE-17271-D - Manual 8-Tooth 3.73 Ratio / White 23 Speedo Gear - $16.75

 

This ^

 

So is the '97 cable driven? Where as the '98 is electronic?

 

99 and up are adjusted by the computer. 98 and down are done by that cable

 

I have a '98 and it has a VSS on the transmission. There is no cable.

 

There is no cable, its a gear driven speed sensor that detects a magnetic pulse and sends it back to the ECU. Its not adjustable.

 

nice. thanks. glad I didnt spend $150! lol

 

You can actually do it either way. On our transmissions you can change the gear drive or adjust it electronically. You just can't do it with a handheld tuner like on the '99+ cars.

 

I like the $16 way lots better than the $150 one !!!
lol

 

It's a very easy swap too. I want to say there is only 1 small bolt holding in the VSS. Pull it out slowly and the gear is right on the end. Swap out the old one with the new one, slide it back in, put in the bolt and your done.

Hell, it would take me longer to get my car high enough to swap it out than the actual swap itself.

 

nice. ty