Have you checked the level and quality of the fluid? That's always the first step in diagnosing any transmission issue.

Beyond that, from prior threads, I'm aware of 2 issues which have caused various A/T problems.

First is ground issues, in particular the ground which is located under the battery tray.

The other one is corrosion in a transmission connector. So it would be a good step to undo and clean the TCU connector, along with checking all of the wiring going into it.