Tires will almost never slip the same amount between the inside and outside bead. This will put a twist in the tire causing all kinds of problems. With as much slip as you are getting you need to put screws in it. Here's a link to the M/t tech for rim screws.
http://www.mickeythompsontires.com/tech.php?bulletin=s4
I have always just used the Moroso screws.
http://moroso.com/catalog/categorydi...?CatCode=25001