Yeah, i used to have that problem when i was playing strategy games, then it was about three years since i had started using computer. Now after 5 of using PC years I've noticed that my hand is warm again ;D
Maybe jou shoud get highers chair, cause i think that when your hand goes down the blood can't reach your wrist ;]
And yeah the grip is very important too, now i hold mouse like a feather not like a real mouse that can run away