i would say check the water pump and the pressure cap....i did a bunch of work on my brother cavi becuase it was overheating...i changed the thermostate, then the radaitor...then the head gasket + water pump and it still fuckin overheated...then we changed the pressure cap and it stopped after a day....he never thought about telling me that the day it started overheating that coolant came gushing out the cap....check them out though...i had coolant boiling in my overflow so i changed the cap and it hasnt ever since