1997 Acura TL Heating Problem The overflow bubling hot

I have chaged the ECT sensor, thermostat, radiator and radiator cap. The car take a long time to heat up when it does it blows cold air and sometime it will blow hot air while driving or idle. When sitting idle I can her the water bubling in the over flow. The overflow antifreeze is at the correct level but can smell outside the car. I am being told it is my head gaskets but Acura Service has checked and said the pressure checks and the head gasket check was fine but can't be if not heating properly. Is there a test where they can tell me if the head gaskets is blown. Acura said they was fine when tested and I paid for service but when it continued with the problem they said the only last thing it could be is the head gaskets. Don't have money to just throw away.