Go a 5 speed Supra , or a 3.08 Diff

[panoz78]

If your running at around 105 @ 3000rpm you have a 3.55 ratio diff .
I've had mine out and defiantly know my ratio,
If you want to check jack it up ,put a mark on the yoke & housing then turn your wheel one turn,
count the revolutions of the tail shaft, 3 1/2 turns 3.55 ..approx 3 and a bit 3.08 .
You could also try different profile tyre eg. 50'series- 60's ,or even larger rim size 14-15's will drop your revs as well
The summit site have a few calculators you could play with as well

http://www.summitracing.com/expertad...mission-lookup

http://www.summitracing.com/expertad...tio-calculator