By Toyota branded, are you sure it was the WS?
If he flushed it completely it would take something like 12-14 quarts. Did you pay over $100 for fluid alone? I guess I'm not sold on your mechanic using the correct fluid or checking it correctly. It seems like something he did had to have caused the problem.
Hopefully the blackstone kit will help you out. Keep us updated, and good luck!
The link posted will not replace all the transmission fluid BTW. You should replace your transmission fluid every 60k miles.