Recently, I purchased a set of Integy alloy rims (direct fit type). I have a GPM ball diff that has worked really well with the stock plastic hubs. It has a full range of adjustment using the standard washers and locknut. On the other hand, the alloy rims tend to cause the nut to back off immediately to the point of total slip. I assumed the nut was worn, but going back to the stock hubs proved otherwise. I have tried numerous washer/spacer configurations with no luck...Any suggestions on the cause? Attached is a photo of the diff layout. Thanks in advance.

-Russ