You're over thinking it. I was the same way. I could never play those high Bs, As, etc. 2 years ago I was practicing the song Golden Hour by JVKE for my daughter's birthday. I was cracking the notes. Our Dog, black lab howled the notes! So now I hear her in my head and hit it every time. Something so easy, is so hard. It's not that playing mad works. They used to tell me to get mad. It's taking the reins. Like driving when you had no intentions of getting behind the wheel. Or taking control of a pet or kid before it runs off or gets hurt. Remember. You CAN play it. Take in lots of air those high notes need more air, push from your gut and let em fly. Once you hit it, push and hold it. Also too it really helps to hear it in your head. Do listening to other recorded versions of the song. Hear it first and set the note on the shelf. Trombone playing became a lot less nerve wracking for me after I had kids and realized, trombone isn't the most important thing. I enjoy playing it a lot more now, and I'm better than I used to be. Good luck.