Well, I fixed it.
I cut a 1" hole in the EVAP case just to the left of the blower motor at the top of the case. That is where the EVAP core lives.
I proceeded to flush out the case with a garden hose and watched as mud ran out of the EVAP case drain. This took about 15 minutes before the drain ran clean.
I now have plenty of air flow!
I sealed up the hole using the piece I cut out and some JB Weld Quick Set.