Hipchip: Thanks so much for the additional information. I'll try to address your points as best as I can.
Ultrasound: I'll ask the PT today if they offer ultrasound at this facility.
MRI: I called my doctor again to get an answer about scheduling an MRI before the end of the year (still waiting for the call back). However, today I will ask the PT if he will recommend a sports orthopedist closer to home (mine is on the way to work and not an easy drive on a day off). I strongly suspect that my injury is worse than the ROM tests suggest during the evaluations; almost every exercise I do, they seem surprised if I'm not able to do them without pain, and they work with a lot of other people to give them a basis for comparison.
Pain vs. soreness: The primary pain I feel is midway between my shoulder and elbow (at the base of the deltoid) and I would describe the pain as sharp. I've been using "mild tearing pain" to describe what I feel. Other smaller pains in the shoulder itself feel like minor tearing sensations. I would describe any of it as dull pain or minor soreness. It seems VERY vulnerable to any activity -- the smallest movements while wrapping gifts, driving (I drive a stick shift). It does not hurt much to sleep on it (the PT says not to anyway).
Cycling: The PT knows I am a cyclist and I am anxious to start training for upcoming rides next year. At first, he said it might be best not to ride for a few months if riding causes pain. Then, he said if I really want to ride then it will take longer to heal, and that is a trade-off. However, I don't want to forge ahead and cause further damage or delay other activities longer than necessary (e.g. rescue rappelling).
That sounds like a muscle imbalance more than anything. The deltoid inserts at the base of the muscle and goes up towards the shoulder, so if it's going down to the elbow it may be something else. Problem is, there are so many structures in the shoulder area and nerves that can be irritated. Carpel Tunnel, which is in the wrist, can be referred to the shoulder, and even being tested by a neurologist is no guarantee. I had pain in my neck and shoulder. They said it was carpel tunnel, then they said it was thoracic outlet syndrome, then it ended up being a herniated disk in my neck, so it's sometimes really hard to tell. So don't get too frustrated, just keep doing your rehab and keep getting checked and they'll figure out what's wrong. Problem is, the body only has so many symptoms it can use, so they have to figure out which one is what as one set of symptoms could be several different things.