I upgraded from P3Dv3 to v4.5 recently and on trying to reinstall your KJFK encountered an error message that told me that the installation could not proceed unless GSX Level 2 Expansion is already installed.
So I downloaded & installed that, but still KJFK refuses to install with the same error message.
On checking I find that the file GSX Level 2 Control Panel.exe is installed in:-
1. C:\Flying\Prepar3D 4.5\Addon Scenery\USA\Addon Manager\couatl\GSX, dated 24 Nov 2018, size 353560 - and in:-
2. C:\Program Files (x86)\Addon Manager\couatl\GSX, dated 2 Jul 2019, size 356056
If one of these is an incorrect location, maybe that is the cause of the problem?
I did try rebooting after installing GSX Level 2 but that had no effect...
Any help would be gratefully received!
Thanks,
Mark