On my '06 silverado i have replaced the thermostat, and the temp. on the engine still isn't where it should be, it gets up to 195 and then it goes to 184 and moves around. I have zero heat, it blows cold not even warm. Could this be a bad water pump? The heater hose coming out of the water pump to the heater core is cold, the other hose at the heater core is warm. I have already ruled out air in the system, I already got it all out. Please help!!!