Finally success. I troubleshoot the vacuum down to the line which connects one half of the check valve T to the vacuum reservoir. The pump was pulling good vacuum when tested at the manifold. When I disconnected the aforementioned line and put my thumb over it I could feel the suction immediately and could also feel the air coming from the panel registers. I used a mirror to confirm that the reservoir was mounted to the evaporator housing without any leaks and when I re-attached the line I noticed that there was about 1/16" of exposed male fitting (line wasn't pushed in ALL the way). Pushed it in all the way and it's all good. The diverter door quickly moves from one position to another and all settings work accordingly. So after 18+ months my a/c issue is finally put to bed.