Put a block under the gas pedal.
I had a '76 c-10 with an almost stock 350/350, quadrajet, 3.07gears, 31x10.50 A/T tires 2 wheel drive that saw a lot of balls out off road. On the street I was always hot rodding it. I was in high school. I'd race anybody just for the fun of racing. I still do in my bird. I got about 8 mpg regularly. But that was 10 years ago when the gas prices were still under a buck. It all depends on how you drive it. If you want good gas milage, put a block under the gas pedal. Or a 2 barrel manifold.