I wonder if your problem originates higher up in your arms or even your shoulders or neck. It could be that the way you sit puts pressure on nerves. It seems you've paid attention to how you hold the needles and yarn, how you move your hands, things like that, and haven't isolated a cause. Maybe posture changes would make a difference. I think it's not a knitting problem so much as knitting adds to whatever is going on already and that's when you really notice it. Maybe a small towel rolled up to rest your wrists on? When I learned to type they stressed good posture and how you hold your arms and wrists, but that was back in about 1970 and I have no idea what is taught now. If you were going to type on a manual typewriter...not only have lots of people never used a typewriter, one that doesn't plug in is freakin' beyond belief!... you had to learn those things.
Some recollections make me feel positively prehistoric.