[Big Dave]

slowmover:
A 4BT3.9 and a T-56 in a F-150 should give outstanding results. They are much lighter than Super Duties. If it were a long bed with a aeroshell, even better. I've been thinking about a 4x4 Expedition with a 4BT and a T-56 for a winter vehicle.

comptiger:
You are right. T-56s can be adapted to transfer cases.

nubbzcummins:
With smaller (like 235-85x16) tires and 3.31 gears you could get awesome MPG. Those big-diameter tires exact a huge price in rotational moment of inertia. You have four gynormous "flywheels" to pour energy into everytime you accelerate away from a light. You have to accelerate those "flywheels" rotationally before you accelerate the truck laterally.