Well, you probably know my stance... Anyway, I would guess that you are "simply" accumulating tension along the way, and you run out of steam in the end. I would suggest to carefully go through the piece and all its technical challenges and the required motion patterns to find those spots where you get tense (the trills, for example, or the octaves, the constant movements to the high notes, etc.). I would not try to overcome these issues by building up and using more strength. Economy is more important than brute force. Good luck!