I had a 1972 half ton with automatic that got about 14 MPG with a 302. I put a Holley 2 barrel carb on it so I could get more power. It worked. AT and AC were the major options along with PS.
To get 14, you need a smaller engine or a different truck. The tires (on the good side) may need more pressure. Sometimes you find 35 PSI when it should be at least 55 PSI. Chances are that you will never see anywhere near 10 MPG.
A car magazine tried to improve fuel economy with a Suburban (about 1977) and did a lot of practical things and got one more mile per gallon. My 454 Suburban got 7.6 MPG, any time of year at any speed. I got rid of it because it took $18 to fill the 30 gallon tank. That kind of money would get you 27 gallons of gasoline in those days.