The advise above is mirrored by my experience,use 4.10s to replace the factory 4.57's. That said, do lots of research on T5's as there are many variations in gear ratios, speedometer drives and even bell housing bolt patterns. The best for our use will have a mechanical speedometer drive and a .72 od (5th gear) and be original to a Chevrolet S10 from the mid to late 80's.
This page is good resource as is our own member, lugnutz. All of His post have a link to tons of great T5 info he's developed and shares.
Good Luck, RonR
