For the new truck to arrive, the fuel point must be at least 3.45 meters high, and we set it as such in the stock GSX configuration for the PMDG 737 which is included in the latest release.
However, if you customized it (even before), and you set a fuel point too low, the old truck will come instead, because your own customizations will always take precedence over the internal GSX data.
So, in order to be sure you are using the correct configuration, go in the airplane configuration editor, and press the "Reset" button, to Undo all your changes and return to the default GSX configuration.