Yep, thats the weak link...3rd & counter..bAAM!
I just got done changing over from 3.5 to 4.1. I run a T-5. Change over to a 065 cluster and you can powershift that sucker(if you wanted) I like the 4.1, but then again I'm running 28" tall tires and a high rpm smallblock with very little low end torque. Try this:
www.smokemup.com/auto_math/mph_range2.php
D&L Transmisions(631)351-4387 Larry- he builds a mean T-5 and other tough manual trannys. Call him up-he shares his knowledge.
Good luck,Ed