I had this same problem with one of my vent sitting to high.
To adjust the "VENTS" to sit flush (at least on my 88), under the vent turn down screws
there is an adjustment for moving the vent mounts up and down.
loosen the mounting screws an move the mount till it is level.
This has nothing to do with adjusting the "deck lid". You only adjust the vents 
Good Luck
-Michael
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88GT/Auto/Beechwood Leather/SunRoof/Wing/JVC-CD-Sub-Woofer/225/45/17 Michelin Pilots/All Opts Ex.T-Tops
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