So is it water flow or air flow???
Or is it water flow AND air flow?
Next time the temperature gets very high, try raising the idle to 1500 rpm and see what happens. If the temperature goes down, a high-flow pump or different pulley may help.
Or you could put a large window fan in front of the radiator opening and see whether that helps, indicating the fan is the major culprit.
But - it could be combination of aggravations...