For the sake of completeness: Why did you replace the master and slave? If it was because of this problem, and you've checked for visible fluid leaks and there are none, then it may be time to pull the transmission and take a look at the clutch and pressure plate. But! I've had to bleed my clutch system a couple times and have found that at first I need to drive it around pushing a couple times to get the clutch to work. But, that after a few miles of working the clutch like this, it gradually gets its old feel back.