tubes clear? Check radiator core for cool areas when warmed up engine off by feeling the core inside the engine compartment. Core should be uniformly same temp all over.
What open degree degree thermostat is in the engine? If yo replace thermostat check in pot on stove with thermometer for just open temp and full open temp. Compare to rating on the thermostat for accuracy.
Do you have an infrared temp gun to check temp at the thermostat housing when warmed up?