gooov

i was driving on the highway and traffic was slow. i tried downshifting to fourth but the clutch had no feel/pressure. I coasted to the exit ramp and came to a stop. i shut off the car, pushed in the clutch, shifted into gear, and started the car. Immediately the car stalled out. The clutch had no pressure and it was rough shifting into gears. I bled the slave cylinder and pressure was regained in the clutch. A week later the same problem reoccurred. We re-bled the slave cylinder and topped it off with new dot-3 brake oil. Its been a little over a week and roughly 100+ miles since we re-bled the slave cylinder. Is this a cause of air in the system or a faulty salve/master cylinder?