Check the obvious as well, the de gas pipe, the small thin pipe that runs from the top of the stat housing to the top edge of the expansion tank is clear, and the cap on the tank is ok, I would also be tempted to pull off the top hose with the engine running(just started) to physically check you have flow from the pump, as the top/bottom hoses will still get hot to some point from pure heart travel through the coolant, just to discount it as a issue.
tabetha