I would run a cleaner thru the trans oil then change out the fluid before you give up on it.
The two that I have used in transmissions are:
1. seafoam (the one made for the transmission)
2. and auto-rx
www.auto-rx.com
The auto-rx is my favorite. it is made from plant easters and gently cleans parts. The seafoam is petro based, and does work wll.