I recently replaced the stock nut on my Epiphone G400 custom with a tusq nut and I'm having one problem with it. When tuned to pitch and intonated, my G string plays sharp (almost half a semitone) on the first 4-5 frets. I figured it was the height of the action at the nut, so I lowered the nut slot a little. It got a little better but I'm still out of tune on the first few frets. Based on how much I lowered the nut slot and the effect it had, lowering it further until it should play in tune would be way too much and the open string would buzz on at least the first couple frets. Am I just missing something here? I'm not really sure what to try next.