When the gear selector display lights up inverse, it means the trans computer is telling you something is wrong. It's the transmissions version of a Check Engine Light. Sometimes the trans will go into "limp Mode" if the right things report failures.
See if you can find someone with vag-com software (the equivalent of the dealer scan tool) and have the trans computer scanned for codes. That may give you enough info to point you in a direction to start troubleshooting.