High Fluid Level
WARNING: This page is about a different car, the 2002 Ford Econoline. However, it is still accessible from the selected car via links, so may be relevant.
A fluid level that is too high may cause the fluid to become aerated due to the churning action of the rotating internal parts. This will cause erratic control pressure, foaming, loss of fluid from the vent tube, and possible transmission failure. If an overfill reading is indicated, drain and refill the transmission.