I think your fuel mileage will be worse if you switch to 3.73s, especially with those 285s. I would change tires if you want better fuel mileage, like say to a 235/85/16....tall and skinny is the way to go for fuel mileage, and they are lighter than the 285s. The tune will help as long as you can keep your foot out of it. A cold air intake and a less restrictive exhaust may help, but it won't be a Prius. Even if you did all of this we're only talkin' maybe an increase of 2 to 2.5 mpg. after that it's all in how you drive. My $.02 worth.I CURRENTLY HAVE A STOCK 02 CHEV 6.0 WITH 285'S AND 410'S IN THE REAR..... WOULD NEW GEARS HELP?
If you're not hung up on the skinnier look of the tire, the 235/85/16 is a good choice, and it works well in practically every situation, i.e. towing, hauling, mud/snow, etc. Probably won't corner like the 285's, but if you want a roadracer I suggest a Z06....I DID NOTICE THE TRUCK DID NOT ROLL AS GOOD AS WHEN I HAD THE VERY SMALL 245/75's ON BUT NEVER THOUGHT IT WOULD AFFECT IT SO MUCH. MAY BE NEXT TIME I WILL GO WITH A TALLER 85 SERIES TIRE AND HOPE THAT WILL HELP THE ROLLING RESISTANCE.
Pushaw! I think the 235s would look ok, especially if it had a good looking tread design. Anyways, we are after MPGs, not show car awards. But I agree with hanging on to the 4.10s. The 265s are better than the 285s for fuel mileage.Don't give up the 4.10's; you'll regret it. 235's?? Wow. Those are small & will look silly; especially after the 285's. Maybe try 265. Actually, your mileage now isn't too bad considering. Driving habits impact tremendously. Pretend there is an egg under the pedal!