I have a 2011 Silverado 4x4 LTZ with the automatic HVAC controls. I bought the truck with 17K miles about a year ago, and now have 43K on it. The first 9 months I would set the temperature at 75 degrees and it would adjust to the changing temp throughout the day. When I got in and started it in hot weather it would blow on high for a while and then slowly creep down to a lower setting, maintaining a constant temp inside as I drive. The last 2 months I have had to mess with the temp setting constantly. Instead of setting it at 75 I now have to set it from 70 to 85 to get it to do anything. If I set it at 75 it blows on high and eventually kicks the MAX setting on. I find I have to keep increasing the setting until I get to 85, at which time it starts to creep down. So, instead of just turning the fan up or down manually I now have to run the temp up or down. It was never like this before. I took it to the dealer 4K miles ago and they charged me $65 to recalibrate it, which of course did nothing. Hopefully someone else has had this issue. Thanks.