Nothing has changed in the refueling process in a long while. I don't know what "the MD-11" exactly means, since we don't have any MD-11 for MSFS supported in the internal GSX database so, I can't say if the airplane has been provided with a proper profile, which has the fuel system set according to the way the airplane works, which can be default or custom.
Because, if the fuel system is flagged as custom ( the "show Fuel/Cargo" option in the airplane profile is Disabled ), GSX is NOT refueling the airplane, the airplane is refueling itself so, fast or slow, it's not related with GSX.
If, instead, the fuel system in the profile is flagged as default ( the "show Fuel/Cargo" option in the airplane profile is Enabled ), so you see the GSX Fuel menu with the various options available, then GSX will try to refuel the airplane but, that assumes the airplane CAN be refueled externally, so it's not running some kind of internal fuel simulation like most of the advanced 3rd party airplanes do. Without knowing how the airplane works, is difficult to say if it can be refueled externally or not, meaning if the option to have it refueled by GSX is correct.
