3 year old - what can we do?

My soon to be 4 year old is experiencing difficulties at pre School and with his general development.
All his assessments to date have been fine for his age. But, the last 9 months have felt like he's stood still whilst other children have continued to progress behaviourally, physically and with their social and communication skills.

Some examples of this are -

Running - he has splayed legs when he runs - meaning he often falls over his own feet.
Coordination - he finds it difficult to hold puzzle pieces and coordinate them into place.He's also a messy eater requiring help to feed.
Listening - he cannot define the letters of the alphabet a - e - each letter he pronounces with a 'f' noise at the end despite my best efforts repeating the actual sound. He can say other letters such as 's' and 't' and 'i' without a problem.
Aggression and hyper activity - there have been cases of hitting, strangling (possibly actually hugging sometimes) of other children at school. He appears to not understand he has done something wrong even when the other child is obviously upset.
He can sometimes whirl up into a frenzy of activity, running, and jumping and having to be restrained.
Sadness and order - he likes things in certain orders, if he gets upset or the order is broken (for example taking a different route home from school he finds extremely distressing), he can become extremely upset, with everything then becoming wrong and bad to him. His crying can go on for hours - it's not angry but real sadness. Massage sometimes calms him down.
Affectionate - he is affectionate with us - cuddles and kisses and requests for stories and to sit together. He has a best friend who is a similar age - who have some (albeit limited) joint play.
Groups - 121 he is fine - in larger groups he finds it difficult to focus and remain still.
Humming - constantly hums little tunes when playing alone.
Eye contact - limited eye contact. I often have to hold his face to mine as I explain something to him (after being naughty or a future instruction). However, if we are playing  and he is engaged then he looks at you most of the time without needing physical intervention.
Most of the time at school he plays alone or is on the edge of a a group.
Language skills - most words are muffled sounding, he does construct sentences but vocabulary is limited. It often feels like he cannot express himself.

I'm about to seek medical help to gain an assessment but interested in any views here please.
I've asked pre-school what I can do to help him and they had no suggestions. It's awful not to see your child struggle this way.
Especially, when I know underneath it he is a loving and capable boy - I just need to help him get it out!

[RockRose]

It sounds like he could stand an evaluation by an OT.  Those last 3 -4  hours,  and will give you a world of information.

Some of his characteristics are just variations - some kids are extremely comfortable in groups,  some aren't.  It isn't a sign of something being "wrong".    It's a personality preference.  

The way you describe his eye contact sounds normal also.

On average,  he sounds like a sweet hearted boy.  I had a child go through OT testing and brief therapy for sort of similar issues,  and you just learn that not every kid is the same,  and some things can be done so he doesn't struggle in school.   Enjoy him and try to relax.

[Agiesmom]

My son is now 11 and was very hyper and impulsive when he was little.  He also did not like change and did not transition well from one thing to another (he needed to know ahead of time, but not too far ahead of time, and it was still tough).  I agree that it may likely be more a personality thing than anything else.

I'd just like to add that you may want to have his hearing checked.  Also, my friend's son was tongue-tied (tongue attached further out, to the bottom of the mouth, hindering the ability to form sounds properly).  I'm sure your doctor will cover those things, but I just thought I'd mention it in case.

Good luck to you!