I reworked mine over the last few weeks. I opened up the main Ac and found all the silver lining tape was gone. I had been finding it(bits and pieces) in the vents so this was allowing the air to go up into the ceiling. I found the vent that is at the highest point was blocked by a big piece of this silver tape.
I bought a roll of silver metal real duct tape(not duck tape). I reworked the main unit and went and did each vent hole with this tape making sure nothing was open to any air gaps around the vent and ceiling areas. Seems to work better but we haven't had the heat yet. Just a thought.
randy