I have downloaded the latest addon manager but it seems Allegiant Airlines is no longer included. What happened?
It hasn't gone anywhere and, as you can see from the Sim.cfg of any GSX vehicle, it has the following assignments:
couatl.icaoprefixes=K KBLI KPGD KFLL KMYR KOAK KSFB KIWA KPIE
couatl.atc_parking_codes=AAY
Which means, it has a score of 1 on any airport in the US, and a score of 4 at the listed airports, and will get a priority boost in case there are several competing operators, if the parking code of the parking in the scenery you use include the AAY code.
Maybe you have the "3rd party developers flagging everything as cargo" issue discussed here ?
http://www.fsdreamteam.com/forum/index.php/topic,14274.msg105217.html#msg105217The latest GSX version correctly makes a difference between cargo and non-cargo operators, so a non-cargo operator won't appear in a cargo parking and vice-versa.
This more realistic logic will of course be confused by developers flagging the whole airport as cargo, usually to get rid of the default ground vehicles.
Which is why, the current update has a new feature, which allows you to override the parking Type in the AFCAD, so GSX won't be confused by 3rd party airports all flagged as cargo or military cargo, on an airport with no assigned cargo operators, which would result in a random operator selected.