Hi Kevin,
I think you're on the money there. The 'doing well in the morning, crappy in the evening' type of dog is usually suffering from Kidney deficiency, which can be an associated condition of Shao Yang disharmony, and also Tai Yang invasion, which you are currently treating. Look at the dog as having had its excesses removed by the existing formulas, and now you're seeing the root condition of Qi deficiency reflected in the pain pattern and the pulse
Given all that, I'd suggest something basic like You Gui Wan, as long as the dog isn't too hot (which is unilkely if it's worse from cold). Continue the formulas you feel are working.
Hope that helps!
Steve