Quick question: When I first start playing, I have no real problems with hand tension on my left hand. But the longer I play, the tighter I end up gripping on the neck. Within 1/2 an hour or so, my left hand actually cramps up so I have to stop. I know I'm gripping too hard but I don't know how to unconsciously stop. Plus, it seems that I have to really push hard to get a clean tone from my barr chords. I don't think the action is too high.

Any ideas for this? How do I go about correcting this?