'05 owners manual states for a properly maintained vehicle, (pgs. 160-164):
* 4.0 L V6, all axle ratios:
4x2: Maximum GCWR 9600 # ; Maximum Trailer Weight 5260 #,
4x4: Maximum GCWR 9600 # ; Maximum Trailer Weight 5040 #.
Follow the "Severe" maintenance schedule in your owner's manual.
Weight-Distributing hitch is required for trailers over 3500 #.
Tongue Weight: Up to 2000 #, < max 200 # ;
Over 2000 #, 10-15 % of Trailer Weight, not to exceed 500 # , Class II,
Weight-Carrying; or 770 # Class III/IV Weight-Distributing Hitch.
Hope this helps!