Sorry to hear about the shoulder problems, Ray. You say that inflammation is involved so I assume that you've been icing it regularly. Have you also tried ice massage?
Sounds like your racket-string combination could definitely be a significant contributing factor. I know quite a few people that have developed shoulder and other arm problems from rackets that are too light. Most of these troublesome light rackets were also very stiff. The general rule of thumb is to go with the heaviest racket that feels comfortable for you, not the lightest. Seems like a lot of ppl that were using rackets weighing under 10 oz are now opting for rackets in the 11-12 oz range.
I've also seen a number of ppl in these forums that have complained about shoulder or arm problems from using polyester strings. Apparently, some of the new polys are better than others. Ppl often use poly strings for only half of of the stringbed -- either the mains or the crosses. They will use a gut or a softer synthetic string for the other half. It is also common to string looser for polys -- at least 10% looser.
Basic Facts About Frames & Strings