Re: Muddy SD '59 neck pickup
The '59's are relatively hot P.A.F. style pickups. They are "authentic" to old Gibson humbuckers, but to the ones that were on the hotter end of the output spectrum. As such, they can block up pretty easily. Try lowering the pickup, quite a lot if necessary. It's OK to go very low, as long as it sounds good; some of my guitars have, at times, had the neck pickup set below the level of the pickup ring. Lower the pickup to get rid of the mud, and raise the pole pieces to get volume back (if needed). It will also help it to sound more balanced if you adjust the pole piece stagger for a better volume balance between the strings.
Simply adding treble won't cure a muddy pickup. It will just add treble and output on top of the mud. What you need to do is to reduce low end.
If the pickup height adjustment doesn't work (though I think it should), try adding a knob for passive bass reduction. If you don't want to add a knob, then you can do this internally, with a capacitor and a mini trim pot. The capacitor filters out bass, and the trim pot makes the effect of the cap adjustable.
