Hi there,
I would definitely get a chiropractic evaluation if there's anyone around there who can do that for you. The behaviour sounds reminiscent of 'vertebral' fixations.
Barring that, the deep wiry pulse and pale-edged tongue with a purple center suggest a need for dispersal. XFHMY can disperse, but SMS tends to pull the blood centrally from epithelial surfaces and so may not be helping here, where the blood needs to be moved peripherally.
What to use? When an animal is comprehensively compromised in its motion, I think first of some derivative of Xiao Chai Hu Tang (Minor Bupleurum). You can use it straight or add Qin Jiao (aka Benefit Hips and Knees from Kan).
If the animal is acting quite cold, or seeks heat, then the other consideration is Xiao Huo Luo Dan. Both of these formulas are moving, which suits the dark tongue. XCHT suits the efficacy you saw of GB points.
Hope that advice gets you somewhere. All the best,
Steve