I recently bought a 1978 Ford F150 4x4 with a 6.6l (400cid) backed by a 3spd automatic. I already know fuel economy is going to be abysmal, how can I boost my mpg?
I would look into an AOD or AODE swap.
Looking for something less expensive though
Install taller gears in the differentials.
Swap in a 5 speed manual.