Makes sure that you get a Dana 44 rear differential, with the 4.0 engine.
Look them over very carefully for rust!
The 1997 through 1999 have some exhaust manifold cracking issues, but can be replaced.
The 2000 have some radiator issues, but can be replaced.
Stay away from the 2005 and 2006, because they have a serious oil pump engine failure, called the OPDA!
The best two years are the 2003 and 2004.........
I would look at craigslist, car gurus, and the truck trader on line...