2008 Torrent AWD intermittent transmission issue

[Vintshave]

I m having atransmission issue. Mechanic says he can t do anything until the car goes into limp mode while he has it. I can t force that to happen. The problem is intermittent. Logic tells me that this is more likely to be an electrical than a mechanical problem. If it was mechanical, it would likely be constant and getting worse. I can go days and hundreds of miles without this issue occurring. Then the transmission starts slipping and banging into gear again. A hard bang causes the ETC light to flash on briefly. A few hard bangs and it goes into limp mode. Let it sit 20 minutes or so and it s out of limp mode.

How do I fix this? I m afraid to go any real distance in this car.

 

[melsg5]

are their any engine or transmission codes stored in history?
does you mechanic have the proper diagnostic tools to read transmission codes?