My truck (see signature) has recently started over-revving when I release the clutch while taking off or changing gears. By over-revving I mean(since I'm sure I'm using incorrect terminology)that when I release the clutch and depress the gas pedal the RPM's continue to rise -sometimes up to 4k-5k- before finally winding down. During this over-revving period it's almost as if I have not released the clutch at all or as if I am bleeding it off very slowly.
It seems to be worse on some days and fine on others but I haven't been able to attribute it to anything in particular as of yet.
Where should I start? Does this sound like a clutch issue or something else?

Please understand that I am not a master mechanic but I'm not afraid to tackle a big job. I've also got friends and family with more knowledge and better tools who can help me as well.