After reading all the posts, one thing I didn't see was truck GVW and weight of truck side by side. OP's truck has a GVW of 9200 I'm quite sure of and if OP weighed truck and it weighs 8900, then he only has 300 pounds left of trucks rated GVW. My old '03 F250 was in same boat w/ the diesel engine. So combined OP can tow 24k, but in legal terms, he's SOL with only 300 pounds capacity.
I'm gonna get blasted here, but we towed rig in sig w/ the '03 w/o a problem. Truck weighed 8500, pin was 1800, 5er GVW was 13,800 (12,800 fully loaded, so had room for 1,000 more stuff). Truck rated for 10k and combo of 20k. With 5er hooked, truck weighed 10800, combo was 21800. Over by 2,000 all the way around. If we were to upgrade 5ers w/ old truck, I wouldn't go above 14,500. With new truck, we are under everything all the around. Again, if we upgrade 5er, wouldn't look at anything much north of 16,000 total GVW. Could the truck tow it? Probly. Just have to be bit more on my toes around traffic.
Another thing to consider. Think: "What if I'm not the driver for "X" reason where I've been used to towing the weight behind me. so have a good idea how to handle it". Now if someone else drives truck w/ 5er w/o a lot of 5er towing experience and you have a trailer that's more than truck's capacity, could be in for a rude awakening in traffic, wind, wet roads etc. Not tooting my own horn here, but I drive semi for a living so I am familiar w/ overweight trailers. Have no problem whatsoever w/ having wife drive at times w/ 5er (both trucks).
Friend had a '05 Chevy D-max 4x4, sb and towed a 15k+ 5er. Yes he had airbags and yes he's towed for sometime now. Had 265 tires. Overweight for truck? You bet! No problems, but the preverbal "What if" always lingered in my mind if he ever rear ended someone.