What fluid are you using? Go with synthetic DOT 4 only. The DOT 3 shit heats up and fails. I had this same problem and thought it was a bad master or slave over and over... turns out I was just using shit fluid. I wasted a lot of time replacing parts when it was the fluid all along. This became especially pronounced on mine after installing headers/CEL eliminators that are hot metal which is even closer to the clutch line.
Also be sure to buy good parts. If you got it at Auto Zone I wouldn't rule out that it's just a junk part. I recommend Japanese made parts only. Rock Auto has a good, inexpensive selection.
Also be sure to buy good parts. If you got it at Auto Zone I wouldn't rule out that it's just a junk part. I recommend Japanese made parts only. Rock Auto has a good, inexpensive selection.