I had this problem also and thought I had the this problem fixed. I still don't have the push back vehicles. I reinstalled the full GSX installation, and the November 2014 vehicle updates, but the push back vehicles are still missing. I read in these posts something about you have to "Update" the vehicles? Am I missing a step? If so, how do I update the vehicles besides the link in the GSX website? I reinstalled GSX, installed the stand GSX alone manager and the November 2014 vehicles updates link. But after doing this, FSX would crash when I would load the QW757. I noticed in my add on menu that Virtuali did not install and I had to re-install GSX again. The QW757 now loads up but still no push back vehicles and now one of the push back crew moves backwards with no leg motion. I feel like I am going in circles.
Update: I saw a post by Virtuali about using the most "Current" GSX installer, which I thought I did, but apparently not, or I did something wrong. I pulled it up from the GSX website and downloaded the most current installer. This time the push back vehicles appeared. So does this mean I do not have to install the vehicle updates in the GSX website to get the most current vehicles? This is where I am getting confused.
P.S. I love GSX ground services and you guys did a great job in designing this.