I am trying to work my way up to some respectable distances as I want to get into brevets and some touring but I get nagging shoulder pain in both shoulders.
Yeah the key comment here is "work my way up."
Usually any upper body pain associated with cycling is the result of "holding" a position for long periods of time. And usually the neck and butt produce more complaints then the shoulders.
Typical advice, back off and try distances that don't produce pain. When retrying longer distances make special effort to "move around" and change grip style often.