I have a 1991 S10 with a 305 in it. The truck had a four cyl. In it when it was made my rpm are to high. I think it has 410 in the rearend. I have a 350 trans (3 speed auto) if I change my wheel size to 20 inch. Will it help me out a lot also im going to put 373 posi. That I already have. Thank you.