please help with my contour transmission problem

I have a 2000 contour. I start the car put it in drive and it goes. but at times I get in the car, start it and it doesn't want to move in drive or reverse. can anyone help?

Being, this seems to be intermitant. I have found most intermitant faults to be electrical instead of mechanical. That being said. It would probably be good to replace the TRS (transmission range sensor) on the transmission. Thats kind of a guess without monitoring the computer data:) If this doesnt take care of it, then maybe someone needs to check the computer system (codes and data)