Another thing to check is the separation between the two sections of the A/C. By that I mean there is cold air blowing out from the coils and warm return air coming back in. They should be isolated from each other.
Pull the plastic frame down from the A/C and look inside you will see what I mean. The factory uses silver tape and pieces of foam material to keep them from cross contaminating. On my unit it was easy for a lot of the cold air to just move across and mix with the warm return air going back up into the coil.
Also there were places where cold air could leak into the "attic" or empty space in the roof.
My cold airflow almost doubled after spending an hour fixing the factories poor workmanship.
Another spot to check are the circular vents. Take them down and see if the silver tape is preventing cold air from leaking into roof space. And see if the ducts haven't collapsed or squeezed down between the vents.
Ron W.