Re: Why my bridge single coil sounds harsh and lots of treble?
If that's the case, then there are two easy things you can do: 1) Don't run the pickup split, and 2) install a Duncan '59/Custom Hybrid, wired to split to the slug coil (standard splitting).
Option 1 is the, "Doctor, doctor! It hurts when I raise my arm like this!" solution. If you don't like the pickup split, then don't split it. You probably just don't like the tone of a split humbucker. There's no problem with not using a feature on your guitar if it doesn't suit you.
Option 2 will give you a beefier split tone, because the '59/C Hybrid is made with very imbalanced coils. The slug coil has a significantly heavier wind than the screw coil. Therefore it sounds closer to a classic Fender style pickup when split. Split an equally wound lower output humbucker, and you get a weaker and thinner sound than a classic Fender style pickup. This would sound especially out of balance with Texas Specials in the other two positions, because they are hotter than classic Fender pickups.