All vents? So even the rear passenger compartment? If so, don't bother with the blend doors. It's not likely both doors went at the exact same time. I would start with a thermostat replacement and burping the system of air. There are all sorts of posts on here regarding that.

If I remember correctly, the rear has a heater core as well. Hmmm, can't really say they would both go at the same time either! To check for a bad heater cores, you should already have signs of it on the passenger floorboard. It should be leaking. To check the operation of the heater core, find both hoses leading into the firewall that plug into the heater core. Start the truck, and both of these hoses should warm up about the same temperature and eventually get too hot to hold onto.

Report back your findings, and we can help you further.