So you are looking to increase gas milage? Or are you looking to improve "drivability"? I assume that meanswers you want more power? I'm just a bit confused as to what you want out of your regear.
I'm afraid you will never get your stock gas mileage back. To many other factors with the larger tires, and lift. Unless you over gear, and baby the piss out of your truck, and never drive highway speeds.
The gears would, however, give you more responsiveness, or "power", but it's going to be up to your personal experience to know if it's worth it.
Just for reference, front clamshells are virtually unobtainable in my area. My only options are ecgs, or a local shop.