4.0L and gas mileage will never get along IMO.
But if you get that you can be like all the high school douchefucks here that go all the fuck out on a Grand Cherokee and never take it off road
WJ's get shit for gas mileage to begin with. The 4.0 is bullet proof, but there aren't too many problems with the 4.7 either. I looked at both when i bought my WJ. I ended up picking the 4.7 because of the 5 speed auto, and it has a Dana 44 out back. The 35 is weak to begin with, and with big tires they are pretty fragile too. The get better gas mileage at 65 mph, but equal out at about 75+. I had the 4.0 for about a week, and decided that i wanted a 4.7. My parents have a Laredo with the 4.7 and selectrac transfer case, NP242 HD, and it gets about 18 no matter how you drive it on the hiway. I have Quadra-Drive, which I do not reccommend, and i get around 16 mpg. I would look for a Wj with the 4.7, and Select-trac. For a build like that, I wouldn't get the Quadra-Drive, but cause the 4wd lock up in the transfer case is a bit unpredictable, and can be a bit to handle in the snow. Plus, they EAT tires.