Is this something I can fix, or MUST it go back to a dealer?

I have a 2006 GMC 2500 truck. The climate (mode) control, now does not work. I have blower speed control, and it appears nothing else is affected. But the problem is I have no directional control,(floor,vents,defrost). I have checked both fuse boxes, and fuses are good. It is a well maintained truck with only 20,000 miles. I am surprised to have this problem so early with this truck.