every kid is different...

the repetive thing is important... hand flapping, spinning objects... stimming... lots of stimming... more stimming

(stimming tends to be a repetitive behavior thats sole purpose is to comfort or soothe the person doing it) somet stimming behaviors COULD be: spinning objects on a string (my son will literally do this 24/7 if you let him, no joke), waving or moving fingers in front of face so as to interfer with light... etc... stimming fills a sensory need or overload basically.
i saw on another board apraxia... which (i dont know anything about it except what was on that post) is severely delayed speech/non-verbal but without other delays. something to look up anyhow...
GENERALLY speaking and i am sure someone will crack me in the head for this

with autism there is a general delay in all developemental areas. not in all cases but in most. and if it is autism there is TYPICALLY

sensory issues involved. our kids find the world we live in abraisive in certain areas so will have issues with certain things... my son absolutely flips out when i turn the vacuum on... screams, cries, jumps up and down... and he is almost 5 so its not normal for his age

anyhow, i am sure that something will come up. either another dx that fits better or maybe it is mild autism or aspergers and with a little bit of help he will be fine. either way if he is doing well in all other areas then i think you are in good shape (comparitively to someone like my son who is so severe that we were told that he is the way autism use to be and that they havent seen a case like him in YEARS)

and maybe just the speech is what he needs or maybe he needs visual cues to process language better like sign language.
have the therapists mentioned sensory intergration disorder? that can mess up speech and is pretty darn curable and may not necessarily affect other areas of development.
ok now i have written the sequel to your book

so, G-Luck!