I have a Epiphone Les paul and For the most part it plays good this is the issue i have with it and its more noticeable when playing arpeggios , At the first fret of the high E string to about 6 on the high E string sounds good but when i move more up past the 6 fret The volume seems to change like lower sounding , I guess it bugs me more than anything, the neck seems ok changing pick up height doesn't seems to change the issue wondering what people think?
I'm going to guess fairly blind and say that you have your string action set way too low, or you have too much neck relief. Check the relief of your neck with a straight edge and adjust the truss rod if you need to. Also, raise the action slightly, so the higher notes can ring out better.