These "dead spots" are spots where the fret is so worn down that playing the string at that fret yields either a horrible-sounding non-note or the note that should be heard on the next fret up. If I string up with .009s, my D and A chords in open position are a complete disaster. Stringing up with .010s seems to still be OK, but I have a feeling that if I do that, the strings will keep grinding the frets down to nothing, so I think my only option is a refret job.