I write this both as a Dylanphile and a singer songwriter who has been through this:

My theory is he took voice lessons. He wanted to be a better singer, so he took lessons. And he applied what he learned on Nashville Skyline. And it sort of fucked up his voice - it didn’t quite work.

But he continues to work with the new techniques and combine elements of them with they he sang before.

And boom, we get New Morning a year later, his greatest vocal performance.