I stumbled upon this thread by pure accident. I'm in complete shock that someone else experienced the same problem that I had with my TR6060 trans in my old 2011 Camaro SS.
OP,
I went for a ride on the same merry-go-round with General Motors. To make a long and painful identical story short, I went a few steps farther than you. My story picks up where yours leaves off.
Refusing to accept the pile of completely idiotic explanations, I took my car to a very well respected hot rod shop. My reasoning was that no matter the outcome, I could always trade the car in should things go south.
Upon arriving at the shop, I was fully anticipating a test drive where I would have to prove the random 2-3 brick wall condition. You can imagine my shock when I was told that no test drive would be needed because they already know what the problem is. What?!
I was escorted into the shop and was introduced to their master mechanic. He had what appeared to be an assembly line of TR6060 transmissions. Pretty impressive to say the least.
After some basic introductions and a description of my issue, he smirked and walked me over to a bench where a TR6060 was torn apart. He explained to me that the issue is caused by a tolerance problem from the factory. Within 15 minutes of hearing the specifics and seeing a demonstration of the problem and the fix, the ONLY known solution is to rebuild the transmission with a starting price of about $3,500. This was a, "stage 1 rebuild" and they had two other more expensive rebuilds for those who needed the strength for high horsepower use.
He went on to explain that all manufactures who use the TR6060 are aware of the problem. Imagine the loss of capital if they have to issue a recall. It's just not going to happen. I have no idea how they know this or if it is even true but the story made sense to me none the less.
Needless to say, this was the final straw and my journey towards a Scat Pack 392 had begun. There was no way I was dumping $3,500 for a transmission rebuild when the car had 10k miles on it at the time.
At the end of the day, it seems that Tremec might be where the blame should be aimed, with the car manufacturer carrying half the blame given the horrible response to something that they are allegedly aware exists.