Hi Amy,
Lots of questions. It may take me a few days to answer them all. Work is extremely busy with no time to spare.
Regarding this dog, however, I would seek chiropractic treatment if you haven't done so already. If there's no veterinary chiropractor in the area, a human chiropractor with an Activator should be able to do a good job.
Regarding a formula, YYRT is a consideration. I would have thought DHJST would help. Basically, though, if the pulse is weak in a giant breed with musculoskeletal concerns, it's the first thing I try.
Another option, however, given that you've already seen one Wind Cold dispersing formula fail, is ruling out muscle spasm. That would make me think of Bu Gan Tang (Tonify the Liver Decoction). Particularly if the muscles in the area felt very bunched or tight, I would give it a go.
Good luck figuring the dog out. In my mind, chiropractic is the top priority and may produce rapid relief.
Steve