I have a 2010 2500HD and I may have an issue with a blend door, the passenger side windshield fogs up when in defrost.
But I will say this, GM engineers are fk'n idiots for setting up the trucks to automatically select fresh air on start up and never allow re-circulated in any position other than in your face. This is absolutely fk'n stupid for so many reasons: it's fk'n hot in Texas so most AC systems are on max cold recirculated all the time, skunks stink, diesel stinks, puking gas motors stink and it should be on re-circulated on startup.
My Nissan allowed this and I NEVER had those problems because Nissan engineers let me choose how to operate my truck and wipe my ass.
