There's bunch of different issues related to this. I had a similar problem when I drove the car cold and jumped on it .. it would drop out of gear and do the same thing. RPM would go up and down but gear will not engage. I would have to pull over to the side and shutdown and turn it back on. It would work fine afterward for a day or two or a whole week. I believe when engine is cold the transmission oil level goes very low and if you have leaky part in transmission you are already too low. It turned out that I had the transmission leak and then when I checked the trans oil it was 2qt low. So I changed the leaky part in transmission and filter and filled her up. Knock on wood haven't had the same issue since then. It drove me crazy but this forum is amazing and full of information on repairs.

Here's the link https://www.crossfireforum.org/forum...-ta-daaaa.html