What gas mileage does a Chevy 1974 k10 with factory 454 get?

A 1974 Chevy K10 with a factory 454 engine will likely get very poor gas mileage, in the range of 8-12 miles per gallon (mpg). This is a very rough estimate, and actual mileage will vary considerably depending on driving conditions (city vs. highway, terrain, driving style), vehicle condition, and the specific configuration of the truck. Factors like tire size and axle ratio significantly impact fuel economy. Expect to be on the lower end of that range or even worse in city driving.