Johnny Corvette

My clutch never goes soft like this. Really! This is the first time something like this has ever happened.

2001 Ram 2500 quad 4x2, 24 valve turbo 5 speed.Suddenly clutch started going soft (doesn't engage fully, hard to shift into gear) if depressed for prolong period or if engaged several times in a row. Strangely it recovers and works fine within a few minutes. I am guessing slave/master cylinder issue - but why does it recover and work fine? Air in the line? It drives just fine otherwise and clutch and gears work great as long as I lay off the clutch as much as possible (coast to stops put in neutral, etc.). Maybe this is common but, anytime I had clutch problems in past with cars it was a slow permanent process - no recovery. Ideas out there? Hate to crack open housing and buy parts needlessly. Thanks! PS - looks like a great forum! Had the truck only 1 year and have had almost no problems. Used mainly as a work truck.