So a little while ago, I picked up a Core Tremonti really cheap. I knew that it wasn't well looked after like i look after my own, but I thought with a bit of TLC I could at least get it to play and sound great. The action was SUPER high. All the string saddles were on their highest settings. There was also visibly heaps of neck relief, and the floating trem sat up way too high. First, I got a capo on first fret, pressed down on the fret where the neck meets the body and used a .30mm filler guage under the 5th, 7th and 9th frets to make sure there was clearance. All good. Next I lowered the saddles so that the string height was comfortable - not too low, not too high. Heights for all 6 strings adjusted using the radius tools as a guide. Lastly, adjusted the screws in the back to make the bridge sit right. Perfecto. Plays great with the capo still on. Take off the capo. Every string is fine, except for the D string. it frets out on the first fret. Re-checked everything. - All seems to be okay height wise. Neck appears straight with a small amount of relief. Noticed that there is a groove on the first fret under the D string. So, this must be why the guy raised everything so high. Can't use a fret rocker on the first fret. Doesn't look as though it is raised. Could there be something wrong with the neck? Perhaps the nut groove is too deep (doesn't look like it's been filed)? What could be causing this?? It's only the D string and only on first fret.