I just got the Cessna 310R because I don't have a twin prop of great quality, and I found that everything about this plane was much better than I thought! But when it came down to installing the GPS I was having a lot of trouble with that. I installed the addon with my Antivirus disabled and I still have this issue. I tried to select the GPS with the MVAMS menu but that did not really work either, it is either a blank area where the GPS should be or the orange-lettered BendixKing panels.

OP has posted to the official Milviz Support forum, so I'm locking this thread.

 

EDIT: just for the sake of information, the problem is that the OP didn't realize that the various GPS/WX options only work if you already own the gauges required...