2000 Mitsubishi Eclipse

About 8 months ago my car felt like the clutch was slipping at higher speeds the problem progressiivly go worse untill it would not move in 1st my thought was the clutch needed replaced I am intermiediete when it comes to car repairs so I grabbed my haynes manual and set to work to replace the clutch unfortunately I was deployed to Iraq for 6 months and now that I have returned I finished what I started but the clutch I took out did not look badly worn I replaced it anyway and the car drove great for maybe 60 miles before again it felt that the clutch was not engaging so I had it towed back to my garage and tore it apart found nothing wrong with the clutch everything was tight so I put it back together and again it runs fine I have not yet taken it off the jack stands as I countinue to troubleshoot the only thing I have found is that the resovoir for the master cylimder was bone dry so I bled the lines my thought would be that air in the lines would prevent you from disengaging the clutch the pressing the pedal however it is a new design clutch any thoughts on what the problem could be
Thank you