The leg jitters:
After moving the pins around, I did not see the same problem. I then removed the servo from the front leg and moved it to the back leg. Then moved the back leg servo to the front.
The problem has not returned on the leg. BUT, the position of the leg (when sitting) differs now, so I think the servo is defective still. See video PiDog_Shake2
The head jitters:
Moving the pins around yielded a similar problem on the servo, not the hat.
So after much investigating, it appears the (2) servo motors may either be weak, or just have to much backlash in the gear drive. The hat appears to be ok.