Remember that the traps perform more than just shoulder elevation, the lower traps actually work to depress the scapulae like John wrote. So you could have an imbalance there. Try this little dandy:
grab a bench and set it up at about a 50 degree incline, and lie face down on the bench with some light dumbells. Perform what I can only describe as a low-rear delt / lat fly. What I mean is you will keep the dumbells relatively low as you squeeze your arms back, focusing on trying to bring the dumbells together behind your back (physically impossible of course, and don't squeeze so hard that you cramp something in your middle back) but hold that squeeze and feel the traps pulling back and down. This exercise not only hits the entire trap system, but also incorporates the rear delt and neurologically helps your body with that feeling of scapular depression. I wish I had a video to show you, but unfortunately I don't. You can also do the same thing with cables in which you would start high and pull low and back. Imagine yourself trying to stick out your chest and really flex the back!
It also sounds like those traps could use a good foam rolling or massage as they are probably tighter than a nun's corset.