What engine?
They did away with the old reliable 4.0 straight 6 in 2005, which in the right hands could do 17 city/21 highway (hands like mine, for example
) and replaced it with a crappy 3.7 V-6 which is rated for what you're getting. And if you have the 4.7 V-8 you're doing very well.
However, at 200K miles, my highway gas mileage has dropped from the 20-21 mpg range to about 17-18.