It could be that your MG is getting worse as you withdraw. You might need to withdraw at really small intervals, such as 1 mg.
It's worth a discussion with your primary doctor. A hands and feet presentation is typical of a B12 deficiency/neuropathy. And although ArtandIron didn't have a vitamin or electrolyte issue, that doesn't mean that you couldn't. It's worth checking out.
The other electrolyte that might be to blame is potassium. Do you have a diet rich in potassium? Are you retaining fluids from Pred?
People can be addicted to the "high" they get from the chocolate itself, but it could also be a sign of a craving for something else.

I quit chocolate two years ago (due to sugar) and haven't craved it since. It's a hard habit to break.
Annie