I just finished putting a 4bta 120 in my 71 chevy 4X4. I have a 700r4 and 31X10.50 AT radials. I am not sure what gears I have I am thinking they are 3.56 or 3.73. My only mod is a 3200 rpm spring. I have checked mileage twice now and am getting 22 MPG. I have accounted for a 10% error in my odometer already. I hear about lots of guys getting 25mpg +. Is there a way to tune the pump for better mileage, not just more power??