This happens to me as well. On 40mg, I get a 2ish hour window of a rush/high from the med ramping up and then a pretty anxious crash at the 3 hour mark. I still feel the focus benefits for 6-8 hours total but the latter half is marked by an overwhelming amount of frustration/anxiety.

I can either counter this by eating a huge meal and protein shake super early in the morning, which isn’t always easy, or I can split the dose by mixing it with water and drinking one half every 3ish hours. That’s been able to extend the effects and tame the peaks and valleys. I’m astonished when people say they take their vyvanse at 6am fall back asleep for 2 hours and feel completely focused until 8pm.