kurnia38, I can think of a few possibilities.
One, since your shoulder pain HAS improved with ART, then you may need more treatments. And you may need them close together (every other day) until you get where you want to be, then maintain that ROM with faithful stretching.
And remember, you don't want your shoulder to be TOO flexible.
Two, you probably need to address other spinal alignment issues that contribute to tight traps (or is it other neck muscles?). Your tight traps (I might have read this on another thread) are almost certainly an effect rather than a cause. Do you have a head-forward posture? i.e., when viewed from the side, are your cheekbones lined up with the collarbones or way ahead? If your head is forward, you're going to have chronic tightness in the neck. But this is often caused by spinal alignment problems lower down, like kyphosis/lordosis/pelvic tilt. If this is the case, you can easily address the true cause.
Third, tension in the neck could be caused by mental stress. No, really, it could. Or a combination of stress plus other, correctable postural mechanics described above.
Fourth, you may have a more difficult problem like scoliosis. When I say "difficult," I mean that I haven't found any exercises or stretches recommended to fix scoliosis (yet).