I changed my transmission filter & oil and have the fluid at level. I was getting a stutter in my acceleration from 0-10kmh & when Id gear down (automatic) down hills it would go in and out of gear really rough after putting it back into drive then all my gears would thud hard. I added like half to a full cup of transmission fluid with my car on while going through all the gears & now the the car is shifting better & running great.

Problem is when I filled my transmission the first time I was told to fill it to the cap and youre suppose to open the drain plug and fill till it spills out a little then it is full. I cracked my pan seal by over filling it last time but my MAIN question is if I over fill by like a half of a liter will it effect my transmission or seals in a BAD way again? After adding more the car seems to be running a lot more smooth and not stuttering while accelerating. I would like to hear anyones opinion.

Are you checking the fluid with the engine running? It should be to the threads on the inspection plug. It can be hard to keep the car level and jacked up to get under it. Fluid Capacity Specifications
Fluid Capacity Specifications (4T40-E)

Application

Specification

Metric

English

Bottom Pan Removal

6.5 liters

6.9 quarts

Complete Overhaul

9.0 liters

9.5 quarts

Dry

12.2 liters

12.9 quarts

Measurements are approximate.

Yeah, I filled it at a pretty level place with the engine warm and running till it came out of the drain plug. But after adding another cup to it the acceleration shuddering & gear slamming is gone. It'* over fill apparently by half of a liter.

The vehicle needs to be level, if need be place jack stands all around the car. Pull the drain plug with engine running, if fluid is a steady drip its good to go. Add as needed at the fill plug.