I have had four or more similar National Steels. On one of these, the pickup went "south" on me. It did a similar thing, losing volume on certain strings. My tech could not figure it out and I tried a variety of strings guage as you did. I can't even use it, but I keep it hoping for a replacement pickup or a solution. I was wondering if the magnetism on the pole screws got differentially messed up. THe pickup still sounds good just unbalanced. [This message was edited by Buck Dilly on 10 July 2003 at 01:57 PM.]