41 ring gear and 10 pinion gear? Yes.
http://www.demandaam.com/technical-support/aam-technical-tips/to-determine-gear-ratio

Your original closed rear axle ratio would be 4:11 for 1/2 ton (3100) truck.


"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."