Agree with Billiebob. My old TJ with 3.07 gears easily got awesome mpg. It was the first year 97 and had pretty small tires. It was zippy, fast and felt so light. I loved it, was my first jeep so it was awesome, even with small tires. Used to be on the Jeep site. Tall gearing is for best mpg. All about compromising. I'd love to lift mine and get some 35's, but I'd rather not throw all that money away. Not so much the mods, but being reminded of it everytime I'd fill up, lol. Maybe if I win the powerball tonight!.
All the things many jeep guys do, Tires with deep tread like mudders, lifts, spacers all push mpg into the gutter. If you want to improve mpg, reverse some of them. figure out ways to lighten her up. Even simply airing up tires a bit higher helps. Tires make a big difference. Look for less rolling resistance, make the jeep shorter/less lift to decrease resistance. But also use common sense, drive like there's an egg under the skinny pedal, on a stick, I use neutral a lot to coast and not burn a lot of fuel. IBut if you spend money to un-mod something, how long till you even recoup that back in savings? Maybe just live with how it is or get something else if it's too costly.