Join Date: Feb 2009
Location: Northeastern BC
Going from 3.73 to 4.56 would theoretically make your fuel mileage worse, not better. Basically, the higher the number the more torque.
My 2 cents -- unless you spend 99 percent of your time on the highway, with the gas pedal to the floor, then I don't think the axle ratio will make much difference to your mileage. It certainly wouldn't save you enough gas to justify the expense of replacing the ring gears in both your differentials. Remember, you'd have to change the ratio in your front diff, as well, to make it match. Gas might seem expensive right now, but it's not that expensive.
How about your tires? Those Nitto off-road tires probably have ton of rolling-resistance, compared to the run of the mill all-season radial tire. Install those on a full-size 4x4 with a big engine, and of course you're going to get worse mileage than a Toyota Echo.
Re: Lockers and LSDs
Lots of people here can tell you more about those first hand. You can install lockers and LSDs yourself. They don't change the gear ratio in your differential, as it uses the stock ring and pinion gears. You can install them in both front and rear diffs, if you're hardcore, but most people just put them on the rear, and that's pretty sufficient. I find with my stock LSD on the rear, quite often I don't even need to use 4x4 mode, whereas I probably would have, if I had an open diff.
If Princess Auto were a real girl, I'd ask her to marry me.