Boiling over

Hi to all, I have just bought a 2002 MG TF 135 it has only done 60000 miles, the guy ibought it from had the head skimmed fitted a triple layer head gasket, new water pump, thermostat,expansion tank cap and radiator, along with all new belts. it drives great and I drove it home approx 100 miles without any problems until about 5 miles from home when the temperature gauge went right up and it had steam coming out of the new cap. I let it cool down and limped home but most of the way after overheating the temperature went back down to just below half way on the gauge, I have drained the coolant and flushed the system put new coolant in and vented all the air out of all 3 points, run it for a while then vented again, today I drove it about 30 miles and it overheated again, then settled down to normal temperature, Any ideas what to check next,im all out of ideas

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