Just as a simple experiment try putting a washer (with a hole) into the hose to the top of the radiator. This will restrict the water flow and allow the water to cool when flowing through the rad. If the engine is new it will run hot for a couple thousand miles, until the rings have smoothed-out the bores. If you don't have a cracked valve seat then it must be your radiator. In the past I've had more than one water pump that appeared to be ok (no woble) but in actuality the impellor was sheared in the middle of the pump body.
