I used to get 20-22 highway on my 4.7. I just had to do heads and now I seem to be getting 17-18 If I ever recover from the head job and am willing and able to spend 5 minutes under the hood I just might figure out why.
__________________ The Past
95 ZJ Laredo 4.0
00 WJ Laredo 4.0 & 4.7
08 WK Laredo 4.7 (traded for tin can) The Present
07 JK Unlimited Sahara
Speak softly and carry a big stick.
We have room but for one flag, the American flag . . . We have room but for one language, and that is the English language . . . And we have room for but one sole loyalty...and that is a loyalty to the American people. T. Roosevelt 1919
I have the 5.2 with 137k and I get somewhere between 17.5-17.6 for an average. It's probably a bit more city driving than highway. If I ever get a road trip in on the thing I notice averages around the the 20 range.
For those that are noticing a dip in mileage here's something to consider. It may not be your Jeep. It could be the type of fuel you fill it with. If you have a favorite place to fill up and use them on a regular basis, it's possible that their gas is junk. I had this issue recently. I always filled up at the same station every week and began to notice a drop off in mileage and performance. A friend of mine said he noticed the same thing with his truck and said he was going to find a new place to fill up and see if maybe we were just getting bad gas. Turns out, he was on to something. Once I changed gas stations my Jeep had better throttle response and fuel mileage.