Traps too large
It sound to me like you may have a case of synergistic dominance going on. What this means is that you have one muscle that is being a bully and not allowing others to do their jobs. In the case of your upper trapezisus, this particular region of the muscle is dominant to your lower traps and adductors of the scapula. So, what can you do about this? Simply resolve to stretching the upper traps prior to your training session, this will put that hyper boy to sleep. For the remainder of your session focus on creating length in your cervical spine and avoid shrugging all together. Be mindful you may be shrugging even when you dont intend to. If your on your computer now take a look at your posture - are you shrugging? Good, then stop... the muscles will get smaller!
