How to tell whether I'm playing 16th notes or triplets at high BPMs

Core question: Why do my sixteenth notes always turn into triplets above 200 BPM? And I want to identify my primary picking motion. I use my middle, ring, and pinky fingers as the driving muscle group for upstrokes. But at high speeds, I can't tell if I'm relying on a compound motion. How do I integrate forearm rotation into my picking mechanics?The text was translated by AI.