My 1992 GMC shortbed came with 3.42 rear gears. I changed them for 3.08 and it has raised my gas mileage about 20%. I am running a 5 speed transmission and the .70 overdrive loves the high gears, runs just under 2000 RPM at 70 mph. The only change in driving is sometimes I have to shift into 4th on some steeper hills on I-5 at the ridge route. I still pull my car trailer with a Blazer on it with no problem.
