[Ackattack]

I put a TPI 350/700r4 combo in my 72 GMC. It had 3.08 gears and 275/50/17 tires (don't know the diameter off the top of my head) and it was a DOG on the highway. I swapped to 3.73 gears and it made it much more pleasant to drive and I picked up 2 mpg (IIRC I went from 16mpg to 18mpg)

I just bought a 91 chevy parts truck for the engine. Originally it was set up with a 700R4 and 3.42 gears. I think this would probably be the most ideal combo for fuel mileage with an auto. A 5 speed would probably do even a little better.

For my 69 that I"m swapping the TBI 350 into, I'm hoping to get close to 20mpg with that engine, sm465 4 speed and 2.73 gears. I have 255/45/20s, but I may have to swap to the 15" wheels to hit 20mpg.