Greg sent me a picture of the reason he missed the Maze and CM2013.
The sound at the rest stop that rainy night just north of SLC was the flex plate flexing where it had broken and the torque converter wobbling. Just too much diesel torque! LoL
Once home - Greg had a spare fly wheel, flex plate and spacer on the shelf, and he just had to order new bolts.
I am glad it was not really serious - i.e., engine internals.