Update on my CCV Saga...
My selling and (normally) servicing dealer confirmed that they didn't have the part and would not order it until I brought it in for diagnostics. They said that they would need the vehicle for 3 days to diagnose, that is even with making an appointment. Made an appointment with another local dealer who said 1-2 days for diagnostics. Second dealer took just over a day to confirm the CCV but part is on backorder with no ETA and that the car was "undriveable". I would be 4th in line for this part at this dealership (with the longest already having waited 30 days) and 7th in line for a loaner car, but that GM would cover $44 per day for a rental.
I went on a hunt for the part. The original dealer said that while they could see that there were some in inventory at other dealers, they couldn't see what other dealers had them - sounded fishy to me. I went hunting for the part and had great luck with some of the smaller dealers helping me out and telling me what other dealers showed them in stock. At the 3rd dealer, I found 2 in stock that were not allocated to customers. They would not sell one to me however, as they were holding them for them to eventually do the repairs themselves. I did notice that both dealers were owned by the same nationwide network, so I hoped that they might be able to work something out. I was wrong!
After again confirming availability of the part at the newest dealer, I went and picked up the vehicle from the original dealer and drove it 30 miles to the new dealer. The drive was almost 100% freeway, so I locked out 10th gear and drove 65 mph. just to be safe. Documented temps and highest trans temp was 172 - No CEL or reduced acceleration warning, so all good there.
Fingers crossed the repair goes well from here. Only downside is that I had to pay the $200 "diagnostic fee" at the original dealership. Going to try to get GM to reimburse that, but don't have a ton of hope on that. Anyone have any luck with that?