There have been a bunch a posts on which gear to pick

It's not just RPM but also the inchs of vacuum that shouldbe considered

With a 235,228,248,You may find there is just not enough torque to support passing and climbing power!
3:90s with a five speed O/D works pretty good cause
you can shift down to 4th and pass or climb.
A 3:55/3 spd/small motor combo may end up a real dog and not get the mileage your looking for.

Just a thought