Celica trannys do shift a little rough compared to most other automatics.
I would drain the tranny fluid (the plug is on the bottom of the tranny pan) & refill (use the dipstick hole & a funnel). Then drive it for at least 100KM. This will help rinse the old fluid out of your cooling lines, cooling core in your rad & the torque converter.
Then I would do a tranny fluid & filter on it. This will clean it right up & you should probably get a lot smoother operation from your tranny.