well, im guessing you have an sd chassis. i run a 106t 64pitch spur and a 32t pinion. with a 6.5, id run a 28-29t witch has a fianl of 8.6(29) 8.91(28). you probly have a 48pitch so for the same ratio, use an 88 spur with a 30(6.90) or 31(6.68)
id start there