I discovered this vacuum hose off, and for the life of me cannot find a place to plug it.. Swear I've gone over every inch of engine where this thing reaches.
Seems to be a consensus that it's the heater control, however my heat and AC work fine, and not just out of the defrost vents as suggested.
Truck is running EXTREMELY rough and have been getting misfire CEL's.
Pictures here show the same as the OP. It's definitely a vacuum, it suctions to your finger.
Mystery Vacuum Hose 1
Mystery Vaccuum Hose 2