I used to get pain in my wrist and forearm untill I moved my elbow out from my body so that my fretting hand moves up and down the fretboard by moving the elbow and wrist as one - from the shoulder. This takes a lot of the strain away from your hand and wrist as the only thing your tendons have to worry about is tapping and pulling off on the fretboard. Also, try raising your guitar up higher on its strap to an 'uncool' level. Most jazz players and classical players have very high guitar positions in relation to the chest and many of them play uber techincal fast passages. It worked for me instantly when it came to playing faster, more easily and without pain. Give it a go!