are you guys in the same city?
are you sure you used the correct cap on your radiator, there are two types of small radiator caps - one is shorter in size which will cause such issues if your radiator neck is the taller one.
as syncview said - if you can hear and see movement of liquid between radiator and overflow tank with engine cold while you press the pipes then you have the wrong cap or really damaged radiator cap neck.
I had a car repaired last week - it was a camry which once had overheated really bad - they already had the head gasket job done and it was also overheating like this - the culprit was a bad radiator cap neck - its plastic had literally melted from overheating and the cap never made a seal on it. New radiator fixed it.