I have a 2000 Chevy Monte Carlo SS with the 3.8 Liter non-supercharged. Was sitting in a parking garage idling with the AC after 20 minutes looked at my gauge and saw it was running hot (almost at the red lines). Replaced the radiator cap as it looked like it was leaking, allowed it to idle for 15 minutes seemed to work okay. Started driving, less than a block vehicle overheated. I put in a new thermostat and it seems to run a little cooler but it still between 215-230 (Normally it would be between 190-205. Last year I put a new radiator and hoses along with another thermostat and two years ago I did a water pump. Coolant is new and I also did a block test (hydrocarbons) and that passed. Any ideas?