95 Ford Contour V6 with transmission(?) problem

I have a 95 Ford Contour with an apparent transmission problem. The car drives fine for about twenty minutes or so, depending on how warm it is. After the engine warms up (it seems), the RPM indicator jumps all over the place, the car lurching along, all the way. If I attempt to keep the RPMs under 2,000, its ok, but I can't drive anywhere far as a result. The vehcile has been taken to three different shops, including a transmission specialist, and everyone has said that there's not problem. Thanks for any help!