I question any response to be right on target for what I understand is your objective. Actually, most of your considerations are subject to personal experience.
"is the ride going to be that horrible?"
This is very subjective. Personally, I prefer a stiff/solid ride. In my opinion, the 19.5s will ride like an auto that has high performance suspension. Not only do you get the added weight capacity, but also much less sidewall flex which greatly reduces tire squirm (TC sway). With the stiffer sidewall, you loose the advantages of airing down.
"I hate giving up my ability to air down and venture offroad a little." I am not aware of a tire that has it all. The effect of not being able to air down is pretty much out the door with the 19.5's. That doesn't mean you cannot go offroad. It simply means you cannot air down. Another consideration can be made that your sidewalls are less prone to damage. Personally, I am willing to argue just how much advantage there is to airing down. My experience and beliefs are that airing down is greatly exaggerated, of benefit yes, but a "you gotta do" no. Many considerations on this subject, in my opinion.
"Am I going to regret this? $3400 OTD is not a light decision. " In my experience, over all for hauling you TC, I think you will be exceptionally pleased. As a daily driver, I really think you will adjust to the stiffer ride.
"only other option is to move to a dually"I had a dually for over 25-years. I bought a 2500 SRW (1996) in 2004, and shortly upgraded to 19.5's. I have over 100,000 miles and about eight years on the 19.5s. I have absolutely no complaints on the truck or the 19.5's. I still have this truck with no issues, but it is getting long in the tooth. Circumstances were such that within the post month I purchased a Duelly. Load wise, the stock tires will be just fine. My concern is the tire sidewall flex. I will b e very disappointed if I have to \go with 19.5s.
As it pertains to off road use, I have been dune buggying and/or 4 wheeling since 1972. I currently have a Suzuki Samurai for my wheeling. My 2WD has got me where I can launch my Zuke. I have to admit, I really do not need a 4x4 truck, do not need a dually, do not need a Quad Cab, but **** I really like my new to me truck.
Wayne