Had an 81 F-150 short bed, 300 Six with carb, 5 Sp trans. Got 27 MPG on the highway, about 20 in town. The wife called it the gutless wonder, "It's so gutless it's a wonder it makes it home". We lived up on a mountain at the time, and I would have to go to first gear to get around the switchbacks. Yet my Jeep CJ-8, and her Honda Civic would easily pull them in second. Used it to pull my little 16ft john boat to the river. Could put the boat in and pull the empty trailer out. But put the boat on the trailer and it would not pull them out, had to take my Suzuki 4-wheeler to take the boat out of the river and up the ramp. Put over 350K miles on it with no major problems.
Traded for an 87 F-150, long bed, 300 six with EFI, auto trans. Got 18 MPG on the highway, 14 around town. Could pull a heavy load, not fast but I could get it there. The boat did not faze it, put it in or out. But moving my track rig on the big auto trailer was hard, but I did it for eleven years. Put over 250K miles on it. Sold it to a teenager, he rebuilt the tranny, and I see it two or three times a week around town.
Finally thought I would get smart and get a diesel, WRONG!!!!!!!!! My new F-350 gets 12 MPG highway or in town.