temperature problems at idle are generally airflow issues, temperature problems at highway speeds are typically water flow problems.
High flow, turbulent water makes for best cooling. Sounds like maybe the radiator is a cork in the system. But it could be a slipping belt, eroded impeller on the pump, weakly opening thermostat, etc.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
