Welcome to the forum
DBT is indeed hard work. It takes a lot of effort to do. You have to work hard when doing DBT, but the hard work pays off in the end. Even after you finish, I think it's something you have to keep practicing.
I used the book and it did take me sometime to complete it as it was hard to sticking to it.
I hope you will get through with it this time. Let us know how it goes when you try it again.