I just purchased a 2012 Yukon Denali, literally 4 days ago, it has 25,000 miles. I stopped at a red light, and when I tried to move forward it simply revved the engine, and would not move! I tried to put it in park and back into gear, and nothing. I tried to turn the car off and start up again, and nothing! I had to have it towed back to the dealer. Once it was there, they told me that it was driving fine, and there are no signs of an error on the computer or mechanical failure. I now have the truck back but i have no answers! I am scared to drive it. Please, if anyone has any ideas, please let me know.
Thank you

I'm wondering if they did find codes but didn't want to deal with it. Transmissions generally don't light up the check engine light, but will post a history/current code. If you know of another shop, take it there and have them put a scanner on it and check for codes.

Thank you for your response! Just one quick question...why would the truck be working again so quickly after it completely shut down? If it was the transmission, wouldn't it still be broken? Could they have fixed it within an hour of it being towed to their lot?

Would that code come up on a diagnostic test done through my onstar account?

The PCM control module'* codes have to be read by a shop scanner.
On star can help with basics like unlock doors etc, but not deep stuff like transmission errors.