i just use a calculator
ps - their trans ratio chart is lame - it don't show any of the manual truck transmissions... so for all you manual GM guys
S-10/Sonoma with NV3500 (RPO M50)
3.49 - 2.16 - 1.40 - 1.00 - .73 - 3.55r
Silverado/Sierra with NV3500 (RPO MG5)
4.02 - 2.32 - 1.40 - 1.00 - .73 - 3.55r
Silverado/Sierra with NV4500 (RPO MW3)
5.61 - 3.04 - 1.67 - 1.00 - .73 - 5.04r
Silverado/Sierra with ZF S6-650 (RPO ML6)
5.79 - 3.31 - 2.10 - 1.31 - 1.00 - .76 - 5.23r