That was my first thought but if the budget is allowing for only used gears I did not think the money for a better trans would be there. A 700r4 or similar would be the way I would try to do it. You could keep your 3.73 gears and still be comfortable and get better gas mileage and less wear and tear on your engine. I have/had a 64, and 65 c-10 with stock gears and a v-8 upgrade and 350 turbo trans, I was pushing 3000 rpm on the highway You can actually see the gas gauge going lower. It might cost a lot more for the trans upgrade but in the long run you will be happier going that route. If its not in the budget just change the gears for now.