I've had that problem on and off for a number of years. It is not rotator cuff for me either, merely muscles that tighten up and forget how to relax. It's in my shoulder, across part of my back and sometimes into my neck. I got hooked up with a massage therapist that specializes in sports pain and deep tissue massage, not the day spa variety, who has really helped. The returns are not instantaneous, but it is non-invasive and non medication, both of which appeal to me.
Diana