how much overfilled
overfilled ATF can foam up and cause slipping issues also as foam/bubbles are useless for hydraulics, it is critical to have exactly correct amount of ATF in the unit. Also make sure there is no trace of coolant/water in the ATF, and if its darkened to a black/brown colour then you are waaaaaaay overdue for change. Its supposed to look like rooh afza sharbat, your trans takes regular dexron type ATF - type IID or III.
It has short service life and when discoloured, it is supposed to be changed out.