72 D series 1 ton crew cab, 4:11 rear, 33" tall tires, 727 trans. When I first got it, single digit mileage all the time, everywhere. After a rebuild, it began averaging mid teens in the city, high teens towing a trailer with a car on it on the highway. One extended unloaded trip from Denver to Phoenix, it broke 20.

The rebuild was nothing too spectacular. Basic rebuild with a balance job and as close to blueprinted as I could get. Used KB quench pad pistons with open chamber heads and ended up with a bit over 11:1. Smallish camshaft that had a little more lift than stock. Heads had a bowl blend. Also used dry film lube on all bearings and piston skirts and thermal coatings on piston tops and head chambers and valve faces. Ebrock performer intake and carb. Spent a lot of time dialing in the ignition curve.

Required pump premium to stay out of detonation. It was a towing beast in the mountains of CO. I could pass cars going up the pass to Eisenhower tunnel while carrying a load. The trip to Phoenix was a steady enough drive to really gauge fuel consumption and speed. Did the best at 75-80 mph range despite taching up higher than I wanted. Unfortunately, the high compression that gave it so much power and efficiency at elevation in CO was its undoing once in Phoenix. Detonation was a constant problem and I hurt it while I was there. Later pulled it apart and found a cracked piston. Rebuilt it at a lower 10:1 ratio. Performance and mileage was down as a result, but it also would live on lower octane.