94 Dodge Intrepid/3.5 L engine/ 6 cylinders

I have a question : I want to know if any one could help me. This car is stressing me out and will soon leave me broke. My car runs good there is no trouble there. The problem is my car overheats. I have taken it to get the radiator clean thath's not the problem. I recently changed the water pump, thath's not the problem. The thermostat is working, thath's not the problem. And just yesterday I changed the catalytic, the catalytic on the car was good, yet when they take it off its to late to change your mind. No one will do anything for free. I have taken it to varios mechanics telling me the car overheats because of all the things that I already repaired. So all those things aren't it. One mechanic told me it might be the heads of the car. But two mechanics have assured me it could not be the heads of the car because they look new, and if it were the heads it would start leaking water in the motor oil, and thats not the problem. WHAT'S THE PROBLEM?HELP![/B]