Why does my transmission gears go out when hot?

What is your question?

The transmission Shifts fine when car is first started and cool. When it heats up (180°-190°) ALL gears go out (even reverse) and the car wont drive. As soon as it cools down even a little like 5 minutes the car will drive and shift fine again for another few blocks. Why? What could be causing this? Why would it shift fine until heated up? HELP!!!!