Guys! I’ve found the answer! It’s gripping the pick between the middle finger and thumb instead of between the thumb and index finger. The pain and motion restriction have almost vanished.
I got the idea after watching one of your Steve Morse videos. I had never noticed that he grips the pick with the middle finger. I missed it because he supports the middle with the index. (I always just found his motion weird and fascinating.) I can’t support the middle with the index because it hurts and restricts. My index finger has to be extended but curved: It looks like a velociraptor’s claw, but it’s good for tapping, which I’ve never been into but now will learn.
Changing the grip has a few downsides. It’s not wholly natural yet. I’m still working on the articulations and dynamics: pinch harmonics, etc. I need to smooth out my funk strumming. I no longer have the middle finger available for hybrid picking, or for jazz chord work that skips strings, or for counterpoint. But I can always go back to thumb/index or finger-picking for that Just like a painter must choose between a palette knife and a brush at any one time. Neither tool can do everything.
I’ve also had to change picks. The Big Stubby slips in the middle/thumb grip. But a 1 mm. Dunlop Max Grip works well.
So I have a new tool, and a world that was closing has re-opened to me. I have your site to thank. Kudos to you!