My 68 3/4 power wagon with 318, 2 bbl, 4 sp, 4.10 gears and 9.50-16.5 tires pulling a loaded 4 horse trailer got 8 to 10 mpg.
Swapped to a 76 360, 4bbl and gained more pulling power and 2 mpg.
55 mph is my max speed for hauling loaded with animals on the hiway.
