He sounds a little like my 6 year old, who has dyspraxia. Does your DS have any articulation issues, or issues with speech fluency? The neuropsych who assessed DS said it's an "output" issue. He has a problem getting his speech out in a fluent way. His speech is slow and the prosody is odd. So his receptive language is a lot better than expressive. He was delayed with sentence formation (although he a huge vocabulary labeling things).
He also had early reading ability, although his comprehension is fine as long as he can choose a correct answer (i.e. multiple choice test) rather than express an answer (unless it's a simple question that can be answered with a few words or sentence).
In kindergarten he didn't really make any friends til several months into the school year. Now in first grade he has a group of friends and is much more social.
If you go for an autism eval, just make sure you go to a good place that doesn't over-diagnose. The neuropsych I took DS to said that if I had taken him to certain centers they might have slapped him with an asperger's label due to his cognitive ability and odd speech/mannerisms (like flapping hands, walking on toes, etc). But he does fine on tests for asperger's/autism and there are no red flags other than the superficial type ones. There is an overlap between dyspraxia/developmental coordination disorder and autism. Wikipedia has a good page.
