[glade8r]

I Have the same car with the same problem and believed it was an electrical problem because it would work fine every now and then.
We replaced the entire ignition switch and lock believing this was the problem. We also replaced all the sensors on the transaxle. Still the same problem.

I discovered a strange solution that might work for you. I drove the car like that for two weeks and finally took it to a repair shop where two mechanics took turns test driving it. They didn't find anything wrong. When they drove the car, the car shifted fine.

I discovered that the problem was in the Ignition switch. If I turned the ignition switch on slowly, the a part of the computer system which controls the transmission would not work properly. It sounds weird but that was it.

So try this:

When you start the car, turn the switch until it clicks once. There will be no lights on the dash and nothing will happen.
Then turn the switch quickly all the way clockwise until the car starts and then release the switch.

with mine, you can tell its working because the shift to reverse or drive is smooth and doesn't bang into gear.

Hope this works for anyone with the same problem.