Check for a vacuum leak on the modulator & also check the part where the hose attaches to the transmission (I forget the name). It's two things that may be wrong. But you may just need to get it checked out by a mechanic to see what's going on.

Sounds like your selector lever is simply out of adjustment. What's showing at the lever isn't what is actually the case at the gearbox.

Your gear box has failed - get it replaced or repaired.

transmission is gone

I have a 2003 Mitsubishi eclsipse automatic. When you put it in reverse it will go forward and in neutral its still in gear. It's not makeing any strange noises the fluid is in great condition. before I actually parked it it would jump up to about 3k rpm before it would want to shift. What could be the problem??