[Richard]

My 72 originally had 373's and 31 inch tires, stock TH350 trans. The rpm was a bit high for me. Around 2500+ if IIRC. If not planning on adding an OD trans with the swap I would go no more than the 373's. Would go 4.10's if planning an OD trans. My engine trans and axle swap with 37" tires and 5.13 gears should put me just over 2k on the highway. Right about where my 94 is. Comfortable at highway speeds with power still available. Great milage will never be attainable in these heavy old trucks with brick wall aero dynamics. All we can get is better performance with a bit more economy than 10 mpg.