We had identical issue with our youngest son. Everything you typed is spot on for us too. Same high IQ, same grade, same med…
I am not 100% sure but we concluded it was hormones. We took him for his annual check up a few months ago and he had grown 4 inches since his annual exam the year before.
Titrating off medicine is not fun. We did it slowly, waited until after finals, and started it over winter break. We are lucky that the new meds seem to be fine.
We switched him to Vyvance (10 mg) and Strattera (50 mg). We were on 20mg of Vyvance but switched him back down to 10mg because he was too quick to anger in the evenings. We have now settled in to this new combination and are hoping it will last us a few years.
Also – make sure you look into taking Vitamin D3 and Omega3’s. ADHD brains need more of this than normal and we did a blood draw and found our son was really D3 deficient. I think adding these pills also has helped.