After three weeks in the shop, we got the car back. I think it was torn down to the bottom like the car above to fix the rear air. I didn't see it but my SA told me it was. I gave her the TSB on the axles, but I think GM had already told the guy what to order so not sure if they are the same as on that TSB. The rear AC works again and the wobble is GONE!!! Hallelujah!! The only thing they didn't address was the loss of power. My SA said the tech didn't see anything wrong with it. I told her that's because it's not his car. This car used to have screaming passing power. Hit it at 40-50 to pass someone and it would fly. Now, it feels like a non-turbo car..Don't know what to do about that. No engine light, no actual driveability issue (except one time, I took off hard from a light, going up a slight incline and the car felt like it was lagging, like something was pulling it from behind)
They also did the TSB on the differential but I was not having any rattling issue.
So that's where I am at. Fixed AC, Fixed the dang wobble but now have no idea why my car isn't as zippy as it used to be. I told my SA I suspected it had something to do with the turbo. Perhaps the wastegate not working properly. Never in recent times have I had a car that spent this much time in the shop.