An '04. 5 would have a GCWR of 23,000lbs, which as JCasper said is the total allowed weight of truck & trailer.
My SRW weighs in at about 7,500 lbs with me and the 5er hitch, so that leaves 15. 5k for trailer, other passengers, and gear. However, that also only leaves 2. 5k for trailer pin weight, passengers, and gear before the trucks GVWR of 10k is exceeded.
5er pin weight should be around 20%, so at best (no other passengers or gear) you would be looking at 12,500 for the trailer. Bumper pulls on factory hitch are only rated to 12,000lbs WITH a weight distribution hitch.