Mine had the same symptoms. I tried everything except new radiator.
The water pump was new but I took it off to inspect anyway. I checked the cylinder wall immediately behind the pump and it had been scored by a previous owners water pump failure. It hadnt cut thru the cylinder wall but it had removed material from the cylinder wall inside the water jacket. I found a whole lot of little balls of rusty matter about the size of a 3/16" ball bearing. There were hundreds of them. We cleaned them out, refitted pump and new thermostat and rad. cap. The car ran cooler but not 100%.
If the above list doesnt fix yours maybe you have a problem similar to mine.