Auto Transmission skipping between 1st through 3rd

I have been having some trouble with this transmission for about 3 months now, the shifting is fine when the engine and tranny is cold, but because of the heat and the temp of the tranny, the tranny is not shifting. I have a 93 Passat VR6 Automatic. Please help, if there is something that I can do myself repair wise, please help, if not, would it be cost efficient to buy a used tranny? YOu migt want to get the opinion of a good transmission shop first. Changing the fluid and the transmisison filter or cleaning the internal screen would probably be the first place to start. I am affraid I dont know to much about them to tell you anymore. I do agree that a used transmission might be more economical. You can find some great used transmission sites from our links page...on the homepage of this site. The thing is that I have changed my filter once and cleaned out the pan and did all those self-do tests. I appreciate your help with this problem and will keep using your services if possible, thank you.Car Repair Talk's forum.