Honestly...how good was the 318...mpg / durability / hp

A short tale of 2 'teens... Picked up a 74 D100, 2wd, long bed, auto and power steering. Unknown gears in the 9.25? rear. Bone stock 318 2 barrel. Got a whopping 10-12mpg no matter how easy I was on the gas, or on the highway or back roads. Empty or loaded for the dump - did not matter. Plenty of power, tho.
The 69 ragtop Fury I had drove for 17 years - stock 318 long block, with the exception of a 340 4spd cam and six pack. 14-16 mpg around town and 18-20 on the highway. 727 and 3.55 8.75.