First my air stopped blowimg on the no 5 posistion. then the other day all posistions went bad later on that day the air blew ice cold and now sometimes i can feel the cold air but it doesn't blow.

Hi, the blower module that is located at the bottom of the heater box, next to the blower motor, above the panel below the glove box, has a tendancy to go bad, possibly overheat, and melt the larger of the two connectors. This can lead to one or all sppeds inop. the module will need to be replaced, and th connector inspected. If the connector is melted, or discolored, it needs to be replaced. A pigtail with wires, and connectors, as well as the resistor, should be available at a local GMC or Chevy dealer. Good luck...Coop

The climate controller, which is located under the glove box is going bad. Part costs around $180. You'll see a bunch of wires going into it. You'll probably see 1 of the wires melted. Which is your #5. You'll also need a new wire plug. The dealerships will know this. I have 5 3500's in my fleet