what gearing ratio do I need for most power and fuel millage in my 79 k10 pick-up

The larger the number, the more power at the rear wheel, the lower the number the better gas mileage you get. Pick what you want. If you want the middle, take that one. Chevy changed rear ends around these years so make sure you get one that will go with your truck. Now power or mileage? Here is something to ponder. You have a lift kit, large tires and aftermarket carb. What are you going to do? Off road and mudding or show and go on paved roads only? Replacement rear ends on line run over $500.00 for a reconditioned or new one. If you want off road and mudding, use the 4:11 gears. By spending the $500.00 for an economy rearend, how much will you save in gas to make up for the $500.00 spent and have a sow instead of a real hog in the mud? Same question of buying a hybrid car for $10,000 more to get 10 MPG better. You need to keep the hybrid for 10 years to realize the difference. The 1979 K10 had these options With V8 engine 3.07, 3.73, 4.11 With inline 6 cylinder 3.42, 3.73, 4.11

just remmber you have to change both front and back gears they have to be the same