I've had my 2006 C6 coupe since 2006. Lived for several years in TX and LA, never had any overheating problems. Moved to MT. When weather is very hot 90-100F and I have the A/C on, the temp gauge creeps up toward the 250 alarm point when I am in stop and go traffic. Not a problem at highway speed. If I shut the A/C off in stop and go traffic, temp returns to normal. Have had the cooling system flushed and checked at my local dealer. They said the thermostat was fine. Any ideas? Again, only a problem in hot weather, with A/C on, and in stop and go traffic.