We don't use our AC very often but sure did over the past few weeks in killer heat. The bedroom wasn't cooling down well and little air was coming out of the vent at the rear of the TT above the kitchen counter.
Took down all the vents. Found one where the ceiling was flopping down enough that the vent didn't push up into the duct by about 1/4" and air was being blown into the ceiling space. Got some 2-1/2" screws and pulled the ceiling up closer to the duct. I also found that the vents weren't sealing well against the duct so I used some self-adhesive foam tape (for doors & windows) around each vent where it pushed into the duct.
I also found that one duct wasn't sealed very well at the AC unit so used some aluminum foil duct tape to seal it properly. (Don't use regular "duct" tape or Gorilla tape as it's not meant for ducts.)
That all made a huge improvement and got the temp. down better and more evenly. However, the 13.5K AC unit just isn't anywhere enough in hot weather and I probably coulda died even when it was running okay. Should have got the optional 15K AC unit when we ordered our TT. :(