If you have been working on things and not seeing change time to take a new look at how you are approaching the situation.
Pro Episode # 21 – Pro-User Request Friday: Not Seeing The Change? You Need a Systems Approach.

Yes, tight shoulders and limited thoracic mobility can be an impacting factors.
Pecs tight?
A couple to start with:
Posterior Shoulder Smash 1
Episode 271: Full Over Head Test and Super Couch
Clear the T-Spine, Now We Can Start Talking Shoulders
14-Day Mobility Challenge | 7 Green Lights | Day 5
14-Day Mobility Challenge | 7 Green Lights | Day 6