mmmm. that's some nice Jeep you got there. Good for Jeepin'... not so much fuel economy. That all time 4 wheel is gonna kill your FE, as well as the 5.2L V8. That thing is a beast.
I'm running the AMC 242 4.0L I6, which I can run low 20's consistently on, but I don't know about that v8.
One thing that I find is helping is a block heater, gives me heat in the morning when it's around -6 to 9 degrees outside (don't think it'll be a problem for you) and help the motor be at optimum running temperature quicker, even in warmer weather. If you haven't done it yet, tuning up your engine will help alot as well, if your spark plug wires haven't been changed in you don't know how long and the engine isn't running as nice as you'd like, changing those will help, also cleaning your throttle body from built up gunk will help, as well as a new air filter.
If you need more stuff, I've experimented with alot of duct tape
but the problem is, the limited actually has painted bumpers and side trim, instead of medium grey plastic, so you might not wanna duct tape that. A grille block helps great too.