It's been nine months and no one has jumped in because it's not that easy to just tell you to replace part "X" and adjust you "ACME" screw.
You might have a shift solenoid that's bad, a restriction causing a change to fluid pressure and quantity affecting shifts or a semi plugged filter. It isn't just a "change this" and everything will be ok.
Hopefully you found a transmission shop that does free test drives and they gave you an informed estimate on what it might take. If so and you post it you can get some opinions on it it sounds reasonable.
Best I can do long distance.