aww hugs hun
there are a few things that came to mind when i read your thread. Only things that maybe you havent thought of, but worth checking to see if these could be the reason for his behaviour

1. Could his behaviour be out of frustration? Lack of language at this age can cause kids to lash out as - he knows how he feels but can express it. The connections between the sides of his brain that tell him that he shouldnt do something and the other side which tells him not to do it may not be developed yet. This can take up until the age of 7 before it becomes a problem and is a auditory processing issue.
2. If he is not sleeping all night perhaps he is dog tired- no easy answer for this i know . But tiredness may be a trigger for this behaviour
3. perhaps there is something in his diet that is causing his behaviour- my kids go out of control on anything orange- i mean no control of their actions and really impulsive/lash out behaviours

i reckon it would be worth keeping a bit of a diary, even for a couple of weeks. write down everything he eats, when he sleeps and how long for and if he has any outbursts, when and what happened before it occurred.

you might be able to see a pattern in black in white that you might not have noticed in real life.
The effect of food on kids can be huge!!! Food as you know can not only hype or make kids more impulsive, but also can cause pain and upset his tummy. grumpy child= child who can lash out!!

also it might be worth taking him to see someone. You know all the peads etc to see but what about something a bit out of left field.Depending on where your beliefs lie, perhaps even a natropath, homeopath, bio-resonance, or even a kinesologists. I know quite a few mums that swear by kinesolology and bio-resonance to settle their kids. Also a build up of some minerals or metals in children can cause impulsive behaviour. Also taking omega 3,6,9 can help as well. A great source is either those chewable vitamins or if you can get it into your boys is flaxseed oil.

a good ole rewards chart might be a good way to start to break pattern. aim for just a good Am or PM session to start with and then all day

sugar levels can also be a trigger as well- diary will help pick this up

i wish there was a magic answer but there isnt. It is obviously worrying you- so now its time to do something about it. Collect your data, seek professional help and perhaps you might find some answers. Kids are very rarely naughty without a reason. Address the reason, address the behaviour!!!
hugs hun and here with an ear anytime!
xxxx