Reminds me of the old one-liner: “So I went to the doctor and said, ‘Doc, every time I lift my arm over my head, it hurts.’ He said, ‘Well then, don’t do that!’”
I’m really not the expert in this department. Maybe I’ll just second what was said before about checking out the other motions. For me, the elbow one was always pretty easy, at least for the single string tremolo.
Are you using some tension isometrically (in opposite directions) to stabilize things or keep your motions small and controlled? Somehow I get the feeling that you locate the pick stroke and then clamp down. I could be wrong about this. If that’s true and Tommo is right about the edge picking, what you could be doing is using pick resistance as a “brake” to keep your motion small and then using tension to set boundaries on the outer travel of the motion. That means the whole thing is a balancing act, depending on how much the pick grabs the string on a given stroke, and you’re stuck micromanaging it, which makes you tense up more or slow down to be more deliberate with each stroke. I think it’s more a matter of finding a fluid motion (even away from the guitar) and bringing that to the guitar, and then refining excess travel or whatever (sort of using “loose, fast and wild” as a starting point). I see a lot on this board about finding the most natural one first, developing that to get a feel for speed, and then working in the other motions.