Had a look at your files, and found two problems:
- You based your files on a very old PaintKit, one that was released in 2012, before GSX even had cargo loaders. So, the SIM.CFG for the Baggage Loader, that has the highest priority on the operator selection, was obsolete and not supported by the current version of GSX, so the vehicle was rejected.
- You must have renamed the MODEL.CFG file for the Baggage loader as MODEL.CFG.CFG, this is usually the result of having the option to hide known file extensions enabled in Windows, so you can get easily confused what the real name of a file is. This made the model invisible, even after fixing the other issue. The file that comes with the PaintKit has the correct name, of course.
- You can't use the MET, MAV and MVA codes for your own airline, because they are already taken and are assigned to "Meteorological Research Flight", "Marina Aeroservice" and "Mississippi Valley Airways". If you want to know which parking codes GSX uses, they are the same as ADE or AFX, the list is the ParkingSpec.dat file in ADE or ParkingSpecs.txt in AFX.
GSX doesn't read these files, it has its own internal database, but the content is the same.
In this case, when you want to add a repaint not included in that list and have its own parking code in the AFCAD triggering an higher score, you must use a code that doesn't exists, for example _MET (as I did in the files I fixed for you). Since the airport AFCAD parking codes cannot be longer than 4 characters, putting an underscore in front might be a good solution.
However, using this method will result in GSX saying "Handling provided by _MET", because if there's no proper name for that code, GSX will just print the code.
If you don't like this, you can always use the full name in the Couatl.atc_parking_codes of the SIM.CFG file, like this:
Couatl.atc_parking_codes=Metroair
This solution will have the advantage of seeing the full name displayed, but in this case, you'll have to remove the _MET code from the affected parkings in the AFCAD, and also remove ALL codes, leaving the parking codes list in ADE empty. This is necessary, because if you leave the _MET code in the AFCAD and have Metroair in the SIM.CFG, they won't match, and if you leave the other airline codes (AA, UAL, etc.) in the AFCAD, they will always "win" against your airline because of their higher score.
With an empty parking codes list in the AFCAD, at least your Metroair airline will have the same score of 4 as all the others competing at the airport, and will have a chance to appear, with its full name. Unfortunately, the AFCAD specs don't allow for codes longer than 4 characters, otherwise we could simply use Metroair as a code, but we can't.
So, in brief, if you want to have your airline to *always* appear at a certain parking, name it _MET in the SIM.CFG files, and edit the AFCAD to have ONLY the _MET code at the affected parkings. You will see the airline being called "_MET" by GSX
If, instead, if want a custom name, name the airline as "Metroair" in the SIM.CFG, and remove ALL codes from the AFCAD, this will have the airline being called with the proper name, but it will only appear randomly, in competition with all the others with the same basic score at the affected airport.
Attached is the fixed set of vehicles.