Ok, so I just uninstalled GSX and still the problem of no taxiway markings or gates still appears to be the issue... I would like to send my CFG file but which file do you need? Let me know and I'll send it to you. I have read through the troubleshooting guide but it's very difficult to find out exactly what I need to do, but I have tried to do this.
I reinstalled the Addon Manager from FSDT to update the Coautl Engine, but this doesn't fix it.
Happy to help further but just let me know what I need to send. I am running FSX:SE.