Usually if you have Upper Cross Syndrome, you will most likely have Lower Cross Syndrome. You need to get a full assessment, ( I highly suggest a practitioner from the C.H.E.K Institute who is a Level 2 or higher). It's not just one thing it could be many factors but the key is Posture!! Strengthen the weak and Loosen the tight is the rule of thumb. If one muscle is out of balance, the whole body is out of balance.
As for rotator cuffs, you really need to see a someone who knows what they are doing, again a C.H.E.K Practitioner is your best bet. Let me know what area you are from and I'll see who is around there who can help.
Also, I would get some Nerve Flushing done. I use the techniques by David Butler. He has a few books but the best one is Sensitive Nervous System.