Another Yukon fixed via BCM recalibration. They couldn't see a TSB# for my AT4's vin nor would it throw error codes so techs think it's working right. But tech could see a calibration update to install which I showed n told manager these posts when scheduling appointment and when I got there. He made the tech do it and its finally, at last, fixed. Others in Dallas Ft.Worth with this problem call Eric he's the drive manager at Classic GMC in Arlington they now know how to fix you up quicker than me.