The good news:
I was able to get home last night and no issues (so far) today.
The bad news:
I've been emailing and chatting with my service manager since the initial incident and he's determined that the throttle body needs to be replaced. Ouch! Guess the SIBL will have to wait yet again...
I had a very similar incident a couple of weeks ago. Temps were in the low -20's and I'd started it with the App. When I came out, it was barely idling. So shut it off and restarted with the key, got the same Throttle and Powertrain messages as the OP and no response to throttle inputs. Fuel...