Airflow or radiator problem?

With summer heating up so is the engine. Temp stays normal at freeway speeds but as soon as I hit stop and go traffic it shoots up. Water pump is two years old. I flushed the radiator and didn't get much gunk out. Both fans are running when the AC is on. If I shut the car off but leave the key on the fans do not run when the car is not. I can't remember if they used to or not.

2001 Pontiac Grand Prix 3.1

I am not familiar with the 3.1 but clearly there is a hear dissipation issue in traffic. My first thought is a potential thermostat problem...not stuck closed since cooler on highway but maybe not opening fully. You could remove the thermostat as a test. Another possibility is the pump is not moving enough coolant...not sure how check to that. Or blockage, most likely in the radiator. Gunk can start to block the lower tubes.

Good luck.

Those fans should come on at about 218F.......since your fans come on with the A/C on, the fan circuits seem to be ok.....