hey,
a year is not to long to practice three diabolos. most people take 1-3 years to learn it.
i think what helps most is learning the hover start. the hover accelerates the third diabolo to a point where it has the same speed as the other two, this will help a lot with the shuffle.
feel free to film yourself and post a few tries here, it's easier to help you if we can see what you are doing.