For you guys that have changed gears, did you have to have the dealer re-calibrate your speedo or did it do it automatically? When I changed gears in my '93 F150, the computer recognized it through its rear ABS sensors. I'm wondering if the Mustang does that same thing. Thanks,

The Boss Hog

 

What year mustang? 96-04 5-speeds you can use a Speedcal to change it. You can find it here.
http://www.partshopper.com/fordmustang/ite...%2D9910&eq=&Tp=

that will also work for a 94-98 auto gt.

For a 99+ automatic, you have to use a chip or have the ECU flashed. For an 05, its probably going to require a chip as well.

 

You can also use any type of programmer like Hypertechs or any like that, but they are a lot more pricey...around 400 bucks, but have a few more options..