J.,
I just want to start by saying that I am not an expert in this at all, so I admit I could be wrong, but as I was reading your post, a couple of things that you said (very intense personality, difficult from birth, the thing about the shoes-even about the pediatrician not having answers for you) lead me to think that this might be sensory processing disorder. I don't know if you've already ruled that out- you mentioned that you've had him to specialists, but didn't specify.
If I'm right, though, it would be good news, because when you learn more about it, you'll have moments (like I did w/ my son who was also difficult from birth) where you'll think, "oh, NOW I understand why he freaks out about X, Y, or Z !!!". Also, an occupational therapist specially trained in SPD can help enormously. Many pediatricians still miss it, BTW.
Here's a really good website that really helped me a lot. Make sure to also look at the symptom checklist. SPD is so different for everybody because there are sooo many symptoms. They are in categories, and a child may have no symptoms at all in one or more categories, a few here and there in others, and many in one or more. The important thing is how much does a symptom impact the person. For example, many children don't like loud noises, but a child with SPD may cry and cover their ears. Other SPD children love excessively loud music or tv. Some SPD children are not bothered by noise any more than a child w/o SPD.
If you go through the check-list and think this could explain your son's difficult behavior, there's tons of information on this site. Also the book, "The Out of Sync Child" is very helpful.
http://www.sensory-processing-disorder.com/behavior-probl...
I hope this is helpful- feel free to PM me if you would like. Keep us updated. Hang in there!! :)
BTW- I like what Martha R. had to say also!