I do have a voice in my head but "it" skips words quite often. When I really get into a book the visual imagery takes over more and I don't think about the voice, or maybe it dissappears, I actually haven't thought about it.

You shouldn't worry about how you read or how fast your read. The important part is that you enjoy it or digest the information, depending on what and why you read.

I also really enjoy listening to the audiobook while I read, matching the speed of the narrator to a reading speed I'm comfortable with.