I got Double High C in 37 Weeks and all was well . . . . . . not.
I have had several strokes and am on a road to recovery. I want that fully understood. But . . .
I've posted this before, but one of the best things that affected my approach for playing high notes on trumpet came, ironically, from playing sax. Although I started off life as a trumpet and French horn player, and played professionally on both, I played sax professionally for a couple of decades and was a woodwind minor on my Master Degree.
When compared to trumpet, instead of going through all this angst and gyrations to produce a high note, I just depressed my thumb. Using that concept of just relaxing and making minor adjustments helped my trumpet range immensely. I didn't overreact, playing-wise, and just relaxed (relatively).
Specifically, and this will vary based on preferences and needs, I got the most benefit from Jeff Smiley's The Balanced Embouchure and the Maggio system. My range increased from an obtainable High C and workable A above the staff, to a workable E above High C and a playable Double High C.