Running hot

This Country Squire runs at a quarter in the normal range and then goes to half and stops around three quarters, not good. That is within a forty five minute run time. Every cooling devise has been changed right before I bought it. The fan shroud was missing, so I replaced that. I have come to believe it is the catalytic converter. It is stated many times on the net that if the converter is bad, the amount of heat thrown back in the engine can cause it to overheat. There is no water in the oil indicating a head gasket. The car got over half today and I had it towed home and now I am having the catalytic converter replaced Friday hoping the problem will go away. Also, even though it was still in the normal range at three quarters, when parked it, the overflow tank was taking on bubbling coolant. Just to let you know, water pump, thermostat, belts, radiator, all replaced. I guess the radiator is okay but looks wimpy. Sure hope it is the twenty seven year old catalytic converters. Let me know what you think. Thanks
Gary Walcott
Ellijay Ga
Need to state that it has never gone to the hot outside the normal range level but even though it stated normal range, I knew that having the needle between the M and the A in normal was not good. There is just one and a half letters left in so called normal range at that point.