Read through the post on how to calculate GVWR and GVCWR. This was a hard lesson for me that you "load out" before you "tow out." I have a 9500 lb tow rating but my actual max is 6500 lbs because of the tongue weight (TW). I'm hauling a family of four so I could maybe squeeze a little more cargo if I didn't have 4 people but my hitch is 500 without a weight distribution hitch (WDH) and 950 with. WDH weighs 100 lbs leaving 850 for TW.
Look at the stamp on your hitch as see but I bet it's rated to 1,000 or less with a WDH. All the other numbers matter but this may be a limiting factor even if you can squeeze a little more room on cargo.
Good news is, that means you should have some margin in GVCWR which gives extra power for towing up hills.
2008 Rockwood Signature Ultralite 5th Wheel
F-250 6.2 Gasser
Former PUP camper (Rockwood Popup Freedom 1980)