> You are describing some of the exercises from the Justin Guitar Strumming SOS course.

Not surprised that these are in there!

> I can do it for a few minutes but soon something like semantic satiation sets in and I get out of sync

Huh, I never actually did that for more than a few minutes at the time (when just using the metronome), I can imagine it gets boring and attention wanders. I did try to do it frequently (couple of times a day, spread throughout the day), but only for two minutes or so.

Anyway, I thought you might have tried all of that already, considering you took lessons and bought courses, but still wanted to throw it out there. Good luck!