Next update: My dealer contacted me on Monday afternoon this week- I just dropped it Monday after hours last week- to let me know that the transmission came in and is now installed. I am ready to go! I cannot express how thankful I am for all that my dealer did for me with no notice- to get me back on the road and save my camping season. So far, the truck runs great, shifts better than it did even when new, and runs cool again as it should. I was very lucky to be home and not travelling, I would imagine that if I broke down on the road my options would have been limited. Fortunately, I was able to bring it to my selling dealer that I already have a sales and service relationship with.
Unfortunately, they do not go into the transmission to determine why it failed as it comes as a complete assembly and has to be returned to the manufacturer as an intact unit. I would have been interested to know what failed in there. Some previous threads refer to a snap ring of some sort breaking, but I just don't know what happened in my case. I am certain that when it made that big "clang" noise, something mechanical inside the transmission must have actually broken since the failure was immediate.
Today, I will pull our 14,000lb 5th wheel for our Memorial Day camping trip. We will travel in the White Mountains of New Hampshire, so I imagine some 9% to 13% grades will find out if I have any issues. At least it will be a good comparison as I have pulled this camper on these roads many times with this truck and my previous one as well.