When you are sure that the engine is reaching overheat (re; Herzog) remember the long string months ago that came down to radiaor fouling due to contaminated coolant? A radiator core is a good filter. The expansion plugs, freeze plugs, core plugs, whatever you might want to call them give excellent access to the water jackets and with an off the car radiator check and flush might be what you need. Whatever, your problem is most likely flow related based on the info you supplied. Thermostat, radiator, fan, water pump all important items and just because the pieces are 'new' does not remove them from the suspect list. Hopefully, you will not need to find out via experience that the new stuff is what is causing the problem because it seems to take about 4X the time to figure out in that case. A proper diagnosis is a good idea. Throwing parts at the car works only sometimes. Warren Anderson Sedona,AZ