I have exactly the same problem. I learned to read extremely early (before the age of 2), and read Lord of the Rings for the first time when I was 7. I devoured everything I could get my hands on.

I never took a speed reading course or lesson, but I cannot recall ever having subvocalized. I find myself hitting 750 wpm on speed reading tests with decent comprehension. Not great, but decent.

To use a computing metaphor, I feel like I'm reading with two threads - one to take in all the words as quickly as possible, and a second one to pick the important ones out of the stream. The first thread is completely unconscious, to the point where if you ask me to find a specific word on a page of text, I can always pick it out within 2-3 seconds.

But I feel like a greyhound, itching to run at top speed. Reading fiction is a constant struggle to keep myself chained, forcing myself to imagine the scene playing out, when all I want to do is speed ahead to find out what happens next. It's like an internal war, and it gets worse at the climatic moments.