I had a 74 Dodge extended cab 1 ton, Camper Special, non-dual open 4:10 gear, rear drive with a 440 and a 727. It had a wood topper on the bed with the top even with the top of the cab. The truck spent most of its time towing an open wheel car trailer. The truck and trailer empty with full fuel tanks weighed 9800 lbs. I had a 66 gallon bus tank in the bed, and the truck had dual Mopar installed gas tanks, just over 100 gallons when everything was full. 8 mpg, always! Empty, loaded for bear, and even with no trailer. I think I got 9 once, I figured I didn't get the tank full. I put nearly 150K miles on the brute. Even with all the weight, and a car on the trailer, the truck had power. When the truck was pulling the 6 mile long 7% grade with a Chrysler 300F on the trailer and parts in the bed, gas mileage was the least of your concerns.

The best gas mileage I ever got out of a Dodge truck (before the 90s Dakota with OD) was with a 400 4v powered old power wagon that didn't have much of the 4x4 stuff remaining. That one was consistently in the 13 -14 mpg range. 360s always got the worst gas mileage (about 2mpg worse) than any other Mopar motor except that 440 truck, but I suspect the 440 truck would have been worse if it would have had a 360,