That's interesting. I suppose the written word is just a visual representation that needs to be parsed, natural that there could be thought processes that overlap and conflict with that process. The only similar experience I have is when I'm learning a new tune on the piano - when following the sheet music my mind keeps jumping ahead and trying to work out where the song is going (and also analyzing how I'm playing), whereas working out the tune and playing "by ear" is much quicker for me and doesn't cause any concentration issues. It's a pretty mild and perfectly manageable thing for me though, I can generally force myself to comply, but it takes effort!

I (sort-of) play bass, and when I learn a song from tab, I'm pretty much just wrote learning. I'm sort-of learning to read musical notation, but I don't really have a visual memory which makes it really hard. It would certainly be a lot easier if I had a lot more knowledge of musical theory.

Playing by ear is much harder for me because I know just a few scales, and I can't hold a note in my head long enough to find it on the fretboard. Knowing the scales would make everything a subconscious pattern.

Mind you, I am starting to think that's entirely an anxiety thing.

You might have success curbing excessive daydreaming with a nootropic like modafinil or even something like ritalin. Some vitamins help too like choline. Also, audio books.

I love the process of reading, but I've found for learning large amounts of material I read it out loud, record and MP3 it, and then listen to it through headphones, so that does work well.

Will look into those vitamins, thanks for the tip!