98 Caravan 3.3 Trans problem in Drive only

:banghead: When taking off in Drive (hard/fast takeoff only) the trans and the shift indicator goes back and forth between "D" and "N". The actual shift lever does not move and if I take off in "3" or "L" I have no problem at all. I have checked the connectors and grounds and have also changed the fluid and filter. If anyone has any clues please help!!!!! The dealership or trans shop can't give me any answers.