Raising the nut only affects the first fret. You only do this if everything else is fine but your open notes buzz.Ibateur said:It could be you need to raise the nut.
The truss rod, the overall natural curvature of the neck, the fret level, and the inherent strength of the neck are all related in this, and without an experienced tech looking at your neck, flexing it, and reading the fret level it's to hard to give advice. Ny gut feeling is that if you upped the string gauge you need to tighten the rod a little but then raise the action at the bridge as well. But if you have some high frets then all bets are off.