could the head gasket let it get up by the spark plugs?
my temp. is fluctuating a lot too... it will go up.. then when i go to lower rpms and give it gas it goes back down all in a hurry

EDIT: also someone spotted out that on my intake manifold bubbles were coming up but im not sure if it was just water that i sprayed boiling over flow oil or what but i bought an intake manifold gasket... i havnt put it on yet tho