Well, this morning I tried again, and....engine and tender traveled around the layout at various speeds for 10 minutes, no problem. I did 'wiggle' the tender's Kinematic coupler and it seemed to hang up once, but right after that I hooked it up and, it ran fine. Frankly, it makes me even more anxious to run the pair because I have no idea if it's "fixed" or I'm going to get a fireworks display at some random moment. I'm just going to run it periodically over the next few days and if it behaves, well, good! I will bookmark this thread for the future though. Just in case. Thanks for your help.
Ted, I didn't have a scotch, but I did have few Oreos and Nancy and I watched the latest episode of "Reacher!"