Help my clutch please
 

My clutch has been acting up for about a year now. It is building up pressure in the line after a hour or so of driving. it gets to the point where the clutch starts slipping. I then open the bleed valve on the slave to release the pressure. then its fine for a while more. I have replaced the entire clutch line as well as the slave and master cylenders. then i replaced the clutch and it is still giving me the same problem. someone please help!!!!!!!!!!!!!!!!!!!