Sounds to me like your DH is right. I wouldn't worry. I think my DS is a bit similar: he often starts a sentence and repeats first few words few times before finally saying it in its entirety. He's 7 and v. bright, I think it's just too many things on his mind, it's sort of hard for him to focus iyswim.
My friend was like this as a child...his parents sent him to public speaking/drama lessons to get his brain to tune into his speech (he thought faster than he could speak) which he says really helped him and made his life much easier.
Thank you - so glad to hear your thoughts. Drama sounds an excellent idea. I may look into it as friends have recommended this sort of thing as it builds confidence generally anyway. dh would love the result if he ended up a confident speaker - ds would def take after him rather than me!