freeze plugs dont come out due to overheating. hence the name FREEZE plug. they pop out when the water freezes in the jacket and expands, thus popping the plug and not your block. i would say either you need to retighten your intake manifold or you have a lose heater/turbo coolant line.

as for your running conditions, check to make sure your ECT sensor is intalled properlly and check the ECU for codes.