I have a 2016 z71 Colorado. this winter the heating system stopped working soon after the bumper to bumper warranty had expired. Took it to the dealership to discover that the temperature valve has a crack which prevents heating of the vehicle. The dealership offered to possible fixes, repair the valve by placing a clamp to close the crack costing $350.00 or replacing the valve al together cost $1800.00 plus taxes. there was a bulletin that GM put out about the problem, but I was never notified by GM. I have since reported the problem to GM, however the bulletin has expired. I am hoping GM will financially assist repair. we will see.
In the meantime, check the cost through an independent mechanic.