Hey I’ve been through more or less the same with you, I posted on here a while ago, I had pain also when hanging from a bar, so its been a long time since i have done a single pull up. What really seems to help me and it seems to be my biggest problem is shoulder extension especially on my right side, even more when coupled with internal rotation which is lost with a lot of this bad t spine movement. Now if you as I have really worked on the T spine movement, you will see that you will hit a plateau, that is when you should hit the shoulder extension, I use a rogue green band, loop it and pass it around my shoulder, take a few steps forward, and then slowly start moving my arm behind my back, and then with that extending it and lowering my position so that there is more of a vertical pull on my shoulder. Couple that with a little rotation of the neck away and you may find some new areas to free.