I would tend to agree that the S10 transmission is a little "light for our big trucks. It is not the horsepower that will lead you to breakage it is the weight. I would look for a bigger truck overdrive unit. As far as your axle the "high gear" (lower number) of the rear end might be alright. I would check the rear end for numbers stamped on top of the center section (normal Eaton MO) and google them.
