Well it is very bad to over fill the trans. The way to check the trans fluid level is get the trans up to normal operating temperature. I am not sure but with the car in neutral remove the trans dip stick and make sure the level is at the proper place on the dip stick. When you have determined that the level is good, place several drops from the dip stick on a paper towel. It should be a nice red color, if it has a bad oder the fluid is burned. I would run some seafoam in the trans then change the filter and pan gasket if needed.