This is a REX problem, not a GSX problem. For some reason the "Disable pushhback models when using GSX" function in the REX configutation interface doesn't work. I've posted the problem at the REX forum, but no one has been able to give a reason or a fix. The only way I've been able to get rid of the REX pushbacks is to reinstall REX WWAHD and choose to disable the pushback trucks in the setup window that pops up during installation.