Well, fortunately I figured out the transmission seems to be ok. There was two things wrong. When I went to start it to move it and uncouple it from the trailer, I discovered transmission fluid spraying at a very rapid rate from a hose that extends back to the rear transmission cooler. The hose had worn through where it was rubbing on the frame rail. I was a little puzzled, because I knew that it was not doing that when I crawled under there and inspected when I was on my way home from the last road trip and the problem started. But I fixed the hose, filled up the fluid and took it for a drive with the camper and trailer still on it. I drove it hard with the pedal to the metal through all the gears to make sure there was no slippage. Everything seemed fine, so I figured hopefully this is the end of the issue. Then when I uncoupled the trailer and backed to the truck into the pole barn, I noticed a trail of transmission fluid on the floor. So I crawled under there and saw that it was dripping from near the front of the transmission, where I had seen it while I was on the trip. So I took the camper off, put the truck on the hoist and cleaned everything up really good and started it up and looked up in there with a mirror and a light. I discovered that the brass fitting that threads into the side of the transmission was leaking, the fluid was collecting on the little lip above the oil pan, and trailing forward and dripping off up towards the front. That fitting has a big steel pipe coming off of it, then on the end of that pipe is a big brass tee with two sensors on it and a brass fitting for the hose to continue back to the cooler. One of the sensors is no longer in use, so I'm going to get rid of the tee to save weight. I think all that weight on the end of that pipe, on that little brass fitting threaded into the transmission case is not a good thing. So I'm in the process of doing that. Then I think it will be fine. I hope.

So my theory is that the little leak developed when I was on the trip and caused my initial concern but adding a a couple quarts was enough to get me 200 mi.. Then when I got about 10 miles from home or so the hose rubbed through causing the massive leak which essentially stalled the truck. But since it was dark out by then I didn't see the massive leak.
Thanks to everybody for all their help and suggestions. But I'm glad I didn't have to pull the transmission!