gmcfan, i'm going through the same thing right now with my truck. The best advice i've seen was the gentleman telling you to take it to a tire shop. Currently running a 225-70r 14 front on a fenton rim and a 245-60r 15 on rear. the rims are 15 x 6. Its the street rod look and a look I want to get away from for economic purposes. The tire man suggested that I keep the look and recomended this. 15 x 6 3 5/8" back space rim on front w/ 225 70 15's front, 15x8 4" back space w/ 275-60 r 15's rear. I would like to go with the same all the way to be able to rotate. He said 255 70 15's. But he said it would change the look of the truck drastcily. As far as rpm i'm sure you already know the taller the less I believe. Hope this helps.
