All I really know about them is the 4.0s supposedly have a better intake manifold than the ZJs, they have a more refined suspension, better ride, lower gas tanks, a triangulated rear axle (no rear track bar), and an optional 242HD. For serious off road use, WJs have better unibodies that don't need to be reinforced. For ZJs, you'd need to reinforce the unibody for very serious off road use.