How do you know it is too hot? Is there a lot of pressure in the hoses? That is do they feel very hard or turgid? Is the block hot but not the radiator?

If you are sure the engine is running too hot for the conditions of use, has the cooling system been flushed carefully? Is there any air in the system? And is the radiator possibly partially obstructed? All of these would lead to poor circulation - also there might have been some history where a stopleak or other compound was put in and this led to deposits and partial block that remained even after you changed the coolant.

In my experience if the circulation is poor or another problem is limiting cooling, the temp gauge will rise on a long hill climb, crowded city driving, or another stress, then go back to normal when the situation changes.