Nothing actually, maybe a small boat or utility trailer here or there. Got the truck to outfit with a Super Pacific X1 tent topper to be a nimble upland hunting rig / overland truck. I've got 3 bird dogs and during bird season, travel between upstate and downstate multiple times a week, so need something that can eat highway miles with good MPGs, can handle rutted out muddy roads, deploy camp in the dark in 5 minutes or less and be a street/daily driver the other 90% of the time. I also need the ability to stealth camp in the bed with the tent not deployed, and since I am 6'2", needed the standard bed to be able to do that. I tried to do it once diagonally in the 5'6" bed of my previous truck (Tacoma), and didn't sleep well at all so wasn't going to try it with the short bed this time around.
Not surprising. Without looking, I'd guess that most, maybe all, of the 1500s have a 15K GCWR, so the towing capacity is less about the ability of the powertrain, and more likely a limitation of the chassis design (frame, brakes, suspension, etc.). Your short bed and gas engine weigh less, so that's likely the 300# difference, since your truck is probably ~5300#, or 300# less than my truck. The same thing applies for payload. If I recall, the highest payload was the single cab, standard bed, 4 cylinder WT trim: smallest, lightest truck with least amount of options, left the most available payload since it wasn't utilized by heavier engines, cab, bed length or options. I almost got one of those, but the wife really wanted the crew cab and honestly, I really wanted the diesel. I think it had a payload near 2K#.