What he said, especially #1.
That said, here's another resource that covers some relevant shoulder info.
Oh good lord where has this thread been my whole life. I have horrible posture that is made even worse by my sunken chest (thanks heart surgery). I will be trying the shoulder dislocations and thoracic extensions and see what happens.
LOL. Its cured. I just consciously flexed all the muscles on my back until it became habit.
At first, it was painful because my upper dorsal muscles were weak as ****. I was trembling from pain for a few days but I just pushed through and I'm A-okay.