Speedometer gear
 

T-5 trans... when traveling at 60 mph per speedometer my GPS says I am doing 55mph. Do I need a gear with more teeth or less ?

I would say you need one with more teeth - it is the driven gear so if it had more teeth, it would spin slower, giving you a lower reading at the speedo.

Use this calculator to figure out what speedo gear you need: https://lmr.com/products/Mustang-Spe...ear-Calculator

Take a look at this screenshot I took showing a stock tire size with a typical 3.27 gear ratio that the ford builds run in Miatas.. the correct tooth count in this case shows to be 20.3 so the tool recommends the black 20 tooth gear (the Monster Miata manual recommends the 21 tooth red gear for this same combination) but either way it falls somewhere in the middle... so you will not be perfect no matter what.

https://cimg3.ibsrv.net/gimg/www.v8m...56ee5d7aa1.jpg