Best solution to fixing shifting problem?

Hello, it's so hard to say what is happening -- you do have an electronically controlled transmission. This means that shifts are commanded based off of input information. There could be an internal mechanical problem, or an electronic control problem due to data that is being fed into the unit. There is a diagnostic routine that requires special equipment that may be only available via Volkswagen dealerships or VW repair shops. I'd recommend proper testing. Of course, fluid changes are a great idea for maintenance anyway -- but I'd guess that this is not a maintenance concern.