I have a 67 c-10 w/stock 292 4 speed w/granny, I have 255 60 X 15 tires on the rear, at 70 miles per hour I,m at about 3,000 rpm's (sounds to high), my current rearend is 3.73:1. I'm thinking of putting 3.08:1 for the highway (already bought parts), I also plan on installing a th350 automatic in the near future, any Ideas or thought's

Thanks