My '52 one-and-a-half ton flat-bed with an air compressor on the back would get 6-6.5 mpg empty or loaded, 'fast' or slow, up-hill or down-hill. Empty (compressor only) would give the 6.5 mpg. But the compressor was probably the full, rated load for the truck- it was a Gardner-Denver 3-cylinder, 105 cfm at 90 psi, and had a 6-cyl Hercules engine driving it at about 1500 rpm. And the whole thing was liquid-cooled- about 15 gallons worth, if I remember correctly.
But your mileage sounds pretty good for your truck.
Harvester
