Ok, first the vitals: '91 Pickup 22re w/161K miles, clutch replaced 3 years ago.

After I shift into a gear at any speed and I rest my foot back on the clutch just a little bit, the clutch pedal will sink back all the way with little or no pressure on it. (I first noticed this in situations where I am stuck in traffic and I have to ride the clutch). With it in this position I can throttle the engine and the truck will continue to speed up, eventually something happens and the clutch will disengage indicated by the engine revving as if in idle. The clutch pedal will eventually come back to it's original position. From time to time it will be difficult to shift into neutral from first gear or reverse with the clutch depressed, I have to let off the pedal and then depress it again to get it out of gear

My thinking is it might have something to do with the slave cylinder? I have done a visual inspection of the master cylinder, line, and slave cylinder but there appears to be no apparent leaks or damage. I believe that is that best that I can describe the trouble, so if anyone has some ideas or help I would appreciate it, thanks!

-Andrew