I can read very fast if the book gets ahold of me, you know, sinks its teeth right down to the marrow. I will fly through a book.
Exactly this for me too. If the story and/or character get ahold of me I just keep reading, otherwise it feels like a chore.
A lot of books feel predictable to me though. I suppose I can only get hooked on something that's really original, and really original is hard to do. What helps is if the characters are interesting and likeable as they often/always are with King.
I just find it hard to find originality in (horror)fiction. For example, when Barker's Books of Blood came out, it was really something else: stories that were truly original. But how often does something like that happen? Has there been something like Books of Blood in the meantime? I have not heard of it.
I think I have to be really stimulated by ideas in stories to keep me reading, otherwise it felt like 'just another story'. I need something 'new' from every book and that seldom happens.
Maybe it's just hard to do truly new things in horrorfiction. Sci-fi or fantasy often feels far less predictable to me.