With the PMDG, if you start a flight and your default save state has the PMDG equipment showing, GSX will first need to send them away, using the PMDG FMC commands, so it will take about 30 seconds for all PMDG vehicles to go away and THEN the GSX vehicle will appear.
That's why it's best to save a new state in the PMDG, with all vehicles already sent away, and use it as default or call it before using GSX.
