My 69 rollback with a load of 97 gmc excab shortbed with bad tranny
and a 88 C3500 2wd 454/400 dana60 rear ex cab longbed..
Pushing about 11,000 lbs between the 2 and made the trip 235 back with them.. 8.9 mpg.. with the stock 77 454 /th400 camper motor
Not bad for a homemade truck...