2010 Chevy Silverado Extended Cab LT. I noticed a couple of weeks ago the windshield defroster was not blowing air out of the left side. I made an appointment with the local GM dealer, diagnosis was a bad modulator valve this was replaced, the shop manager called and said they had replaced the modulator but still did not feel enough air was flowing from the left side, so he reprogrammed the A/C Module, they were still not satisfied with results. The shop manager then looked under the dash of his similar body style and equiped truck they were different. Why would GM put a smaller defroster that does not cover the sides and corner?