millighost: this is the problem:

to JCM a shoulder properly, you need - in the least - 6 JCMs.
shoulder up-down, down+forward, down+back / up+forward, up+back.
up-down is a simple deltaadd JCM. you can then make a forward and back JCM, but unless you are doing something magical theres no way to make forward and back JCMs that look perfect with the shoulder either up or down.

to do a proper shoulder fix you need to make one forward and back JCM for the arm up, and another separate set for the arm down.

and it needs to be rigged so that:
IF shoulder forward, and up-down dial is <0 then use JCM down+forward
IF shoulder forward, and up-down dial is >0 then use JCM up+forward
and the same for up/down+back