Remove any grills and even look at the furnace area for deteriorated foil tape. When working on my ac years ago I found that most of the tape was deteriorated and cool air was blowing into the roof cavity.
Recently I removed the duct elbow between the furnace and the floor sheet metal. It had a large gap that was blowing into the floor cavity and the tape was bad. Mine also has separate hose ducts besides the metal floor duct.
The tape doesn't last forever but the general application and missed gaps was pathetic.