I was recently fighting with a similar problem;
The clutch would get progressively worse as I drove it until the point I couldn't even shift OUT of gear.
What it came down to was us replacing the master, to no avail, then cutting a hole in the floor (XJ's suck when it comes to space) to get the slave out. My dad didn't want to return it just yet (brand new; just replaced clutch too), so he went on a hunch;
He "Primed" the slave by pumping it a little while pouring hydro fluid in it while OFF the jeep, until it was full to the threads and there were no more bubbles, then we just put it back on and bled the system as normal. This time the bleeding was WAY easier and faster, and everything works now!
In short, take the slave off and "prime" it, then reinstall and bleed everything again before you blame other parts and get stuck when replacing those doesn't work...