95 Bronco, 351W, E4OD, 4.56 gears, 35x12.50x15 Patagonia MTs.
As stated, the airflow stopped in my vents when I was driving uphill under load for 30 seconds or so. After letting off the throttle, the vents promptly regained airflow. There is no obvious vacuum leak, with KOEO, the vacuum holds the dampers just fine for well over a minute, and tested after waiting, has enough reserve to cycle the damper from max ac all the way to floor and back again. I verified the vacuum check valve was operating and it was, although intermittent failure could be possible. The infamous white hose has been repaired, but cannot cause this issue, as my F350 has a broken white hose and does not have this airflow issue. Any other ideas for places to check?