[wirlybird]

UPDATE:
I think we found the issue. It seems that the glue that bonds the dash together over time has oozed down to cover the opening for the defrost between the dash pad and where the underlying duct meet.
When you look down into the defrost vent from the outside of the truck you can see this green stuff covering the vent opening.
Tried to post a picture but it won't let me.

Now to figure out how to fix this.
Dealer wouldn't touch it due to the age and unforeseen issue in removing the dash pad.

Going to check with a body shop to see about a fix.