Abomination, first I want to say you have an adorable parrot there, and IMHO a very cooperative one. It's hard to reach the level of trust that your bird obviously has with you. You said he had no problem stepping up the first two months? That's pretty normal and that's also why the first months with a new parrot are called, 'The Honeymoon Phase'.
When his behavior changed, did your feelings change too. Parrots are like sponges, they pick up on our moods and react to them. He appears to be very comfortable with you, and that could be why he's pushing his boundaries. I think you have the right idea to go back to square one with training. I wouldn't allow him on your shoulder until you've worked through his stepping up issues. Try keeping him on your hand or forearm while you work with him. Have you tried clicker training? A new approach is more likely to be affective and keep your student focused. You also said he's molting, that causes some birds to be especially grouchy. Another possibility for the behavior change could be your bird is reaching sexual maturity. If it's hormones, the good news is you'll both survive. Good luck and if you have a chance to make a video of his progress, I'd love to see it.
Now he steps up pretty well, but only if HE wants, but usually he is fine.
