2000 concorde overheating
 

I have a 2000 concorde 3.2L that is overheating. we have changed the thermostat, water pump, all upper gaskets and had head shaved. we have flushed the radiator and heater core. still after idling it will shoot boiling water out of the radiator reservoir. what next???? mechanic thinks it is a cracked block. bought this in april broke down on 5/6 and still isn't running. the oil is not milky. i am at a loss somebody help me please.
a very distraught single mom:(