There are a few other things that can cause the symptoms that you speak of, not as likely as air in the hydraulic system, but worth checking.I've run into all of them personally, on early bronco 2's, second gen ranger, and a 90's f150;
1] the masters' ear that bolts to the firewall is broken. Allows the master to flex. Hard to see the crack unless you have someone operating the clutch pedal while you look at the master.
2] Firewall has a stress crack. Again allows the master to flex. Again hard to see unless you pull back the carpet.
3] Like 96zjlaredo says, excessive wear or breakage on the clutch/brake bracket.
4]One other thing to check is that the black rubber gasket under the master resevoir cap didn't get sucked down tight and then somebody filled the wrong side of the gasket with fluid. I did this before I new much about the plastic resevoirs. It looks like the res is full but it's not.
Checking these out is free and doesn't take much time.
Next I would bleed the system. If that improves things it means that the slave or the master is wearing out and will need replacing in the near future. When I was broke I ran a f150 with a leaking slave for months, filling the master as needed. I got real good at telling when it was just about out of fluid.
Good luck,
Richard