GSX only works if I uninstall Traffic 360. Any suggestions?
Uninstall Traffic 360. Or, probably better, asking in their support forum why GSX works normally, until you install their program.
This is what most people would probably do here, it they found a case when, installing GSX, would stop another add-on from working.
An educated guess might be, their products is doing something to "clean" up parking spots for some reasons, perhaps to reduce AI congestion, and it's not correctly filtering non-airplane vehicles as it should, so it can't make out ground service vehicles from airplane vehicles.