96 Taurus LX tranny problem

We've got a 96 LX with the Duratec motor. The transmission has intermittently started to shutter in between shifts, and once in a while the "O/D off" light on the dash will come on and flash. When this happens, you have to stop and turn off the car and restart it for it to stop flashing. If you manuall take it out of O/D, you sometimes can't get it back into O/D unless you shut off the car and restart it. The transmission fluid is fine, and it really doesn't feel like it's slipping, more that it just isn't shifting correctly. The owner's manual says that that the flashing light indicates an electronic malfunction. Will replaceing the PCM solve our problems? Can you simply buy the module and plug it in as a replacement, or does it need to be programmed. Thanks in advance!