What you have described is not an over run from a shifting issue, which is what an additive may correct.
If you are going to try an additive, which is not going to hurt anything at this point, I would try K&W Trans-X in the blue bottle.
https://www.amazon.com/402033X6-Trans-X ... B000M8NZA2
You can do a search for this product and read reviews, YouTube, ect. When you drained the fluid, how did it look and smell? Did you change the transmission filter? Slipping in a transmission is generally caused by burnt clutch packs or bands in the transmission. These go bad over time with lack of maintenance. Internal seals start to leak so the pressure to apply the clutches and bands drops, which causes slippage and the facing on these parts burn up. If the car has not been driven very long with this condition then the above additive may help the seals and get the pressure back up so the clutches and bands have the pressure they need. Drain the fluid again, pull the pan off, check the bottom of the pan and magnets in the pan for debris. Replace transmission filter. The reason for this is that the filter can get restricted and also cause pressure loss and increased wear on internal transmission parts.. The filter should be changed as a regular maintenance item. Put in additive and top off with transmission fluid. Cross your fingers and give it a try. If fluid smelled burnt, damage is done.