I created this page to help customers with gear selection. Doesn’t matter how much power your motor makes if you have poor gearing where that engine isn’t in its powerband then its still going to be miserable or lackluster to drive. Up to 2500 rpms @ 70mph your not turning an excessive rpm and with most overdrive transmissions you can run a lot more gear than came stock and if you change tire size you need to factor in that affect on the overall gearing affecting that rpm number. I chose 70mph as that is a good cruise speed. if you run faster you know your going to be guzzling fuel and well none of us like to drive slower. Going to put some common transmission gears ratios here for you so that you can play with the calculator. I use this to calculate shift points for the computer controlled transmissions.
700r4 4L60E ratios: 3.06, 1.63, 1, .70
4L80E ratios 2.48, 1.48, 1, .75
TH400 ratios 2.48, 1.48, 1
TH350 ratios 2.52, 1.52, 1
NV3500 5spd manual ratios. 4.02, 2.32, 1.40, 1, .78
NV4500 5spd manual ratios 1992-94 1st gear 6.34 1995+ 5.61, 3.04, 1.67, 1, .75
SM465 4spd manual ratios 6.54, 3.57, 1.57, 1