Wow slammie, yes, our little guys sound very similar! Your description fits exactly how DS can identify the cars and his first drawings lately are already of cars, ha. He also seems to refrain from talking cars with his friends. I've heard him give it a try: 'Hey there's a Honda Odyssey!' but then the other kid will say 'No, that's a van!' and he quits trying.
He doesn't stim but he does line up cars around the house quite a bit and he sometimes flaps his hands with he's excited. He also has always shown very very little stranger anxiety and never had any issues at drop off at any sort of daycare/preschool situation. He does love to explore new environments and always seems to gravitate to the edge of where he's allowed to check things out before he returns to the activity at hand. None of it really feels that unusual though to be honest. He mostly just seems like a happy, confident little boy who is very curious about the world. DH thinks I'm nuts for worrying about anything.
I think maybe my main worries are not so much ASD but whether I need to look out for him feeling isolated from his peers and need to pursue getting him into some sort of specialized environment or something like that. I may be projecting a bit though - when I was young we moved a lot and I was always the smartest kid in my class and felt like I was a 'weirdo' (probably a lot more than I was actually perceived).
May I ask why you decided to have your son tested for Asperger's? Or did it come up in some other context?
