This has been discussed and answered so many times and, of course, it's not a GSX problem.
The Fuel truck of course is coming from a scenery "FUEL" parking ( would you expect otherwise ? ), and will take ( by preference ) a path made of "VEHICLE" kind path, so it will do a realistic route with less chances to crash into AI airplanes.
However, it's possible the scenery you are using might have the following problems:
- There are no parkings of the "Fuel" kind. In this case, GSX will use a generic "Vehicle" parking type, assuming there IS one in the scenery. If even a "vehicle" parking is missing, GSX will have no other choice than to spawn the fuel truck from a random parking at the airport.
- Even if the appropriate parking spots are available, they might be very far from your gate, so it might take a while for the Fuel truck to arrive
- Even if the appropriate parking spots are available and are not very far, they might not be connected properly with paths of the "vehicle" kind, either because these are missing, or because a path using them to reach your gate might be much longer, As I've said, GSX will use vehicle paths by preference, even if they are longer than a simpler path made by regular taxiways. Taxiways are only used as a last resort, if there's no other choice.
So, in general, if the scenery AFCAD is made properly, with Fuel and Vehicle paths well distributed around the airports and with proper paths of the Vehicle kind that can reach every gate/terminal, you would't have to wait too long.
If you thing you are waiting too long, it's sure the AFCAD has one of these problems.