A-500 With Reverse Issues

I just installed my A-500 and Reverse wants to play Hide and Seek. The forward gears are fine. I put it in Reverse and you can hear the transmission engage, but will barely move or catch and begin to move. Other times it acts like it's in Neutral.

I want to inspect and clean the valvebody and adjust the bands. Would that help or do I have bigger problems? Do I need to use a specific fluid?