1. Stairs do not spawn. Request boarding GSX removes attached PMDG stairs but is not spawning its own.
Works fine here. Of course, being a cargo airplane, you are only supposed to see a cargo-style stair, and only if you are not extended the airplane own airstair.
2. refueling truck asks to set fuel over and over after I set fuel it does not read it
Works fine here. As discussed so many times, on the forum, on the manual, and with a video tutorial showing how refueling is performed on airplanes flagged with a custom fuel system, the GSX refueling won't start unless the fuel quantity you set with the airplane FMC is higher than the one you had when you called the refueling truck. It's probably best saving a startup state with a very low fuel quantity, so you won't be confused by this.
3. right rear cargo door does not open on first loading/unloading. The main cargo door GSX will open again after the main and front right cargo are unloaded and doors closed.
There's seems to be a problem in the PMDG SDK documentation: the event code for the main cargo is wrong, not sure if it's an error of the documentation or the airplane, but we'll fix this in the next update.