Don't own a EQ6 but .... are you forgetting to tighten (enough) the clamping screw/s that grip your dovetail bar ? Didn't the mount come with an instruction manual ? Here's the online version
http://www.opticstar.com/download/As...EQ6-manual.pdf
Use some elbow grease on it to make sure it's a good tight grip if you don't the OTA will slide off the top of the GEM's head.