[95GTS]

What gear ratio are you going to use? If you go with 3.55s then you can use the 21 tooth speedo gear. Otherwise if you go 3.73s or steeper get the mechanical speedometer compensator. The 21 tooth is the biggest you can put in the T45. The T45 has a 8 tooth internal drive gear. The 23 tooth, which some will recommend and by the way will still not be totally acurate, will be destroyed in a couple months because it DOES NOT mesh with the 8 tooth internal drive gear. You would need a 7 tooth internal drive gear for it to work but you can not get a 7 tooth for the GT T45. Only the Cobra has a 7 tooth in the T45. I"ve already been thru all this with my 96 so I know. If you go 3.73s or steeper and want your speedometer and odometer to read correctly you will need to get a mechanical speedometer compensator. I know Dallas Mustang has them. Other things needed for the install are the pinion bearing, crush sleeve, ring/pinion, pinion nut, shims, friction modifier, and rear gear lube (80W140 I believe is the weight Ford recommends).