Simple to overload actually, 2004. 5 DRW 4X4 with 98 gallon Transflow tank, 133 gallons on board, me, the wife, back seat with gear and the fiver at 10-11K, 2200 on the pin, puts the front axle at 5140 lbs. (7000+ on rear).
My opinion as to the weakest link, Ball Joints, they will wear out sooner than you think if you load it and use it and its a 4-6 hour ordeal to change them out, not tough, you just need a puller, a press and patience.
My '03 went through 2 sets (plus originals) in 120+K and 4 Alaska Trips.