I have noted that my hands get slightly sluggish/jittery/off with too much caffeine. Caffeine works by forcing you to release adrenaline, which a performance also does. So try cutting your caffeine consumption before a gig, bearing in mind caffein has a biological halflife of 5 hours.Is it nervous when you feel fine, perfectly confident, but your hands don't work? That's what I get and there doesn't seem to be any remedy for it.
Otherwise, I think calming techniques can help. But unfortunately if adrenaline is too high, theres nothing I know of you can do but wait it out.