if your t5 is a '88 it should be 7t drive, you need a 21t driven
you cant correct a 8t trans beyond 3.55

and if someone swapped your 7t to a black 6t, then you need an 18 which is what you might have already. or if the trans is ever out...pop the tailshaft cover and replace the drive gear with a 6t

 

my car with 275/40R18 (which is a 27" tire vs a 26") tachs about 2500 at 70mph with its 4.10's and the same .68 OD gear