I can't speak for your child, obviously, but I wanted to be sure that you're aware that fast and GT don't necessarily go together.
Case in point: My DS7 is a DYS kid, but he is as slow as molasses in January! I, too, worried that there might be some problem. But a big part of why he is as he is clicked into place for me when I saw his WISC scores: while he had a PRI score that qualified him for DYS, his processing speed was only 109. Aha! That means he's got an amazing depth of understanding, but he processes the info to get that understanding at the same speed as any ND kid his age. Well, no wonder stuff takes him longer!
When he was still in public school, I'm not sure he ever actually finished an assignment that the teacher gave him. Some of that was because he was underchallenged. But some of it was because he's just slow! His first grade teacher used this to try to undermine his GT ID, too, so it can be a real problem.
My usual description of DS7 is that he's deep, but not fast. Timed tests are awful for him. Everything takes longer than it seems like it should.
Since we're now homeschooling, I've learned to work around it as if it were a learning disability, though technically, it's not. But to moral of the story is that he needs time to process things. If he gets that time, he comes up with some amazing connections and solutions to problems.
Obviously we work on speed, too, but it's not our primary focus. It's a weakness we need to bolster, so we do small bits regularly to improve it.
Your child may have a 2E situation, but from your description, I don't necessarily see anything that screams 2E to me. Especially the way he sometimes stops when he's reading, it sounds to me like he's just thinking...
I'd suggest that perhaps your son is like my son: deep, but not fast. Not all GT kids are.
I'd say that your best bet is testing to see where the numbers fall. The WISC made my son make SOOOOOO much more sense! And achievement testing paired with IQ testing would help to tell you if there's a 2E issue happening there. I'd recommend it.
If you want more details about our experience, let me know. I'm happy to help if I can.
