Hello R. Fizer, for what it is worth, I was in the same situation with my 1966 C-10. It had a Turbo 350 behind the 327, and factory 3.73:1 gears in the rear. With 225/70R15 Dunlops all the way around, I was buzzing 3600rpm on the tach trying to keep up with traffic.
I put a 1992 spec 700R-4 automatic overdrive transmission in my truck, and switched to 245/60R15 BFG's. Made all the difference in the world. Now, in 4th gear(overdrive) with the torque converter locked up, I am turning 2300rpm at 55mph. Much better.
Seth K. Pyle
