Hi OtterMan
I can certainly relate to your frustrations. I know for me, the hardest part of making progress was learning to relax. I realized not all that long ago that I am almost 40 and until very recently had absolutely no idea what the words "relax" or "fun" actually meant. Even when I thought I was relaxing, I actually wasn't. My body might have been sitting in the sun or something, but my mind was still going non-stop. It sounds to me as though this may be a trouble spot for you as well, especially from your comment about the view in the mirror. That was me, I did that every single day. My main TMS spot is my left shoulder and when it's been at it's worst there are visible physical differences. The primary reason for the visible differences was simply because I was catering to it. The right side was forced to do the majority of the work so the left side naturally atrophied. And the part that would make me absolutely crazy would be the days I would look in the mirror and truly wonder if I was going to get up and fly away one day since my shoulder blades looked much more like wings on a bird than something that belonged on a human.
Your posture responds to your emotions, which is why it would look different from day to day. Forward, slumped shoulders, head carried down, back rounded is a "protective" posture to a perceived threat. It's the body's natural attempt to defend the organs and preserve life. When you're upset with yourself, depressed, or feeling anxious, your posture reflects the feelings. Days when you're feeling better you'll notice your head is higher, your shoulders are pulled back and your back is straighter. It's suggested in several books I've read that assuming this "better" posture intentionally can be an effective first step to getting your emotions to follow suit.
On the plus side, the fact that you know you can sit in a car for 5 hours w/o pain, but can't bear 1.5 hrs for a live performance is a pretty good indicator that the TMS diagnosis may be quite accurate for you. Also, we're very prone to treating ourselves the absolute worst when we're exhausted, not to mention all the emotions that come with that. I encourage you to listen to your body. If it's telling you it's exhausted, allow it to rest. As hard as it is to actually do, try to stop "fighting" all of the feelings, the pain, the emotions, and see if you can just accept that it likely didn't start overnight and isn't likely to end that way either.
I struggle to be kind and compassionate with myself and I've found this website to be extremely valuable in helping me to learn how to do this and why it is so very important to learn.
http://live.soundstrue.com/selfacceptance/ . I found the 4th interview in the series to be incredibly powerful, you might enjoy it too.
You will enjoy life again. As hard as this is going to be to believe, the reason you can't do it right now is actually because you are trying too hard. We've all been there and we're here for you.