A 427 will run 75 all day long. But the faster you go, the more gas you will burn. And it depends on the wind. With a wind like we had in Texas yesterday, a wind hitting you in the side would cut your fuel mileage in half. Guys used to put drag axles on them and haul 80,000 lbs gross and get about 2 miles to the gallon. I wouldn't count on more than 5 or 6 pulling a gooseneck.
