I finally fixed it today. I have checked the check valves numerous times along with the cruise control, never could find anything. Was digging around in the truck today again looking for the elusive vacuum leak and it dawned on me (I'm a dummy) that the recirculation door for the A/C hasn't worked since I bought the truck, the actuator doesn't open or close the door behind the glove box, I have the recirc door wedged closed with a dowel. I took the vacuum line off the actuator and plugged it and took it for a drive. Wacky vents finally gone! Hopefully this will help someone else in the future fix theirs.

 

Hey, glad you got it solved. I wonder what the dowel was doing in there in the first place...

 

..what part of Texas....

 

I put the dowel in there to keep the recirculation door shut against outside air for MAX a/c, because the actuator that opens and closes the door is broken. I just never snapped that the actuator was vacuum powered and that was my vacuum leak. I'm northeast of Houston.