The next thing I would definately check is the fluid level, like everyone said. The auto trannies can act very very weird it the fluid is even half a quart low. I truly hope you don't need a new tranny but if that 'O/D Off' light is flashing you may have a serious problem.
I'm not sure if the tranny I got was brand new or a reman from Ford but it is a shiney new case! Cost was $2059.42!
