More horses take more gas if you use them. Back in the 60's, I pulled a gasoline tanker and a grain trailer with a GMC with a 371 cu. in. Olds that would run 75 mph. I averaged 2 miles to the gallon. Field trucks that brought grain from the farm to the elevator with something like a 270 GMC, 261 Chev or 292 Ford averaged about 5 miles per gallon.
