Rob, I'm not gonna pretend that I'm anyone that close to a "specialist", just try to throw some ideas to help isolating the problem.
Just poping up in my mind that there's something can be done before touching the tranny:
1. Scanning while driving (with INPA or GT1).
2. Hook up a multimeter (or more simpler, a pilot light) to the actuator electrical connectors.
If fault reported, or the pilot light is flashing like in a disco then the problem is electronic.
After ensuring all controls and electronics are fine, we'd touch the mechanical.