May be denial?

My son is almost 4 and since he was an infant we have been watching him very closely. He has 2 cousins, one with Asperger Syndrome and the other with Aspberger/Tourettes Syndrome. Needless to say...we've been a little obsessive regarding watching for clues to see if he is displaying any symptoms. We had him screened at 18 months because of his repetitive behavior such as lining up toys, walking on his toes, spinning....all classic symptoms of autism. However, because of his good social skills, great eye contact and his ability to engage in pretend play, we were told that they would hesitate to say he was on the spectrum at all.

He is still highly imaginative and has good language skill. We have noticed in the last month or so that he is starting the repetitive behaviors again. He babbles an sings ALL the time...even when he rides his dirtbike, you can hear him singing away. His fine motor skills are not good and he needs to be touched alot. He is chewing on his arm and shirt alot and although much better now, he drools. I only found that I could check off about 1/3 of the list but am still concerned. What could all of this mean...should I worry?