Since I sorta hijacked another thread with my own issue,
I thought I'd be better off starting a new one.
About three days ago, my 2SS started to shimmy and vibrate slightly. It definitely wasn't a road condition and I couldn't feel it in the steering so I began to think it was a transmission issue. Over the next couple days, it got worse and I could start to replicate it on demand.
Symptoms were shaking and vibration under light acceleration and cruising. Particularly around 1000-1500 RPM, primarily around 4th gear and then to 7th and 8th. Oddly enough, 6th wasn't as frequent.
Also, while cruising around 70mph, it would randomly feel like I was driving over small rumble strips. It would also feel like it was slipping a bit. It was horrible in V4 mode. So I would put it into manual shift and bring it back into V8 mode and shift when I needed but it still shook and vibrated.
Under harder acceleration, it felt like the trans was slipping and the gears felt like they were hanging slightly between shifts.
Took it to the dealership today and after the Tech easily confirmed all my symptoms, they called a GM Tech line that advised them to flush the trans three full times with a special fluid and the replace the filter and refill with new fluid. The dealership didn't have this particular fluid on hand so they had to order it and that will take a few days. The Advisor I am working with seemed surprised they told them to flush it. He fully expected to have to replace the Torque Converter. He did tell me after the flush and refill, they want me to drive it for at least 200 miles to see if the problem continues. If so, they will move immediately to replacing the TC.
Personally, I understand the escalation to try to fix it. But both my Advisor and I think it's going to be ineffective and they will likely replace the TC shortly thereafter, if not the whole transmission.
I'll keep everyone posted.