We have a test car, 2012 Gt auto, that's had intermittent problems- you could drive it and it would randomly stop holding gear, almost like the converter is slipping. Leave for the night and the next day it would be fine. Not temperature dependent from what I understand, completely random. It has an aftermarket, higher stall converter and is tune corrected for that. We did some chassis dyno testing with nitrous to test converter lockup, and it all went well no random trans problems. Converter lockup clutch was fried (which is what we were trying to do for the test) so it was pulled to install a new one. While the tranny was out, we sent it off to get looked at/rebuilt/tested. Got everything back and installed with new converter and fresh trans, same problem- only this time it's staying. To move it around the shop you have to rev it to at least 4k for it to even begin to move under it's own power, and get a pretty good running start to even think about driving up onto the 4 post lift. With data logging, you can see the pressures are good in gear as well as being able to "feel" it go into gear. It feels as if the converter isn't getting fluid almost (second converter, same problem). Thought maybe it could be the trans leadframe issue I've read about causing it to start in 5th gear, but it does it in reverse also so I have my doubts. Any ideas? Maybe a wire has been pinched taking the tranny in and out a couple times, or moving the harness around loosened something? I know the TC fluid pressure is all internal probably but I have abosutely no idea what to check out next.