Well, I read every single post before replying
Honestly, I can't really relate with guitar (since I can't play at all - oh wait - I can do a G chord). I sing bass, play bass, piano, and drums. But where I really notice what you're saying is with the drums.
When I'm soloing, stuff just comes straight from my subconscious somewhere and makes my hands do things - If I actually slow down or force my brain to think about what I'm doing, I can't even keep a 4/4.
For me, the only thing I can say is that I can visualize what I'm going to do a millisecond before I do it - kind of a "zone" or "tunnel vision". For years, I was frustrated that I couldn't physically play everything that my body wanted to play - that problem has become less and less severe over the years, but still shows up occasionally (I doubt that any human can play an instrument perfectly).
The ultimate battle, for me, is making sure that my chops are always prepared to be able to play whatever they're supposed to.
Composing is a whole different monster, because I can never seem to recreate the awesome arrangement and polyphony in my head onto paper.