Ex-Forestry Service truck, designed to carry bulldozers and other heavy pieces of machinery in the event of a forest fire.
It’s a 500 CID Naturally Aspirated Detroit Diesel, has a three range, thirteen speed transmission, plus three more in reverse, and a lockable twin screw rear end. (Normally power only goes to one axle, flip a lever on the dash and they all start pushing.)
It has a funny action to the bed where gravity does as much of the work as anything. Very clever, but can raise one’s heart-rate a bit.