Low Fluid Level
WARNING: This page is about a different car, the 2004 Ford Econoline, 2004 Ford E450 Super Duty, and 2004 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
A fluid level that is too low may cause the fluid to become aerated due to the churning action of the rotating internal parts.
A low fluid level could also result in poor transmission engagement, slipping, malfunction and/or damage. This could indicate a leak in one of the transmission seals or gaskets.