Great to find this thread - I was just thinking of starting one myself about my 5yo DD - so is intelligent, loving, funny, motivated, independent. AND THEN she is a fury, violent (hitting/kicking/throwing), moody and increasingly prone to tantrum when things don't go her way (at home - she isn't like this elsewhere).
She is also highly sensitive to clothing, labels, noise etc. And a fussy eater.
It is MUCH worse when she is tired. And she would be mortified if the teacher knew about her behaviour (to my shame I've used that as a tool to get her to calm down before). I will talk to her new teacher as suggested up thread - thanks.
We are having a very difficult week -but she's just had 3 nights at her fathers over the weekend and he puts them to bed when it suits HIM i.e. very late. And then he calls me saying he is concerned about DD1's behaviour! He refuses to link it to all the late nights he selfishly provides.
Of course it's not just the late nights, but they exacerbate the bad behaviour. We have almost recovered sleepwise from the weekend - and it is Thursday! It's exhausting.
I've found tackling her head on just makes things worse. She has also started attention seeking behaviour - ripping books, drawing on bedroom wall and floor in thick black marker 
, cutting soft toys - none of which she has ever done before. Talking about this quietly after the event, she said she did it as she wanted me to tell her off.
She does get lots of affection and attention. She is quite high maintenance. I have a 2yo DD also and sometimes DD1's behaviour is quite regressive - she wants to be a toddler too. DD1 to her credit is 95% of the time a wonderful big sister. But I do worry what she might do in that other 5% sometimes.
A week ago she was having a major tantrum in the car - it just got worse and worse. She was sat behind me and kicking my chair over and over, harder and harder. Throwing books and toys at me - I was driving! I thought she was going to break the drivers seat. Eventually I pulled the car over, got out of the car and slapped her on the thigh! I don't usually smack her, but I really was at wits end. loud noise, but no mark. BIG MISTAKE. It had the desired effect of stopping her violent behaviour and leaving the seat alone. But since then when she has been naughty she says she wants me to smack her 
I feel doubly dreadful. I won't do that again - it just makes things worse.
So my tactics now are 100% just staying calm. Explaining how I feel, giving her space. Not ignoring her, but not feeding the bad behaviour with attention. The worst thing I can do is get cross - she loves it! 
I struggle with that.
I also don't engage in the argument with her. DD1 "I want XYZ." Me - "well we can't do that today because we are doing ABC. We can think about it for another day." DD1 "BUT I WANT XYZ" (repeat x 100). ME - I stay silent or I say "I've told you how I feel about that already".
She does get lots of affection from me, from her childminder and teachers, other family members, from her sister and friends - she is a very tactile affectionate girl.
No doubt splitting with XP at Xmas has made things worse, and does his attitude (blame me, put them to bed late, drop them off late i.e. do what suits him, the girls and I be damned!). Not much I can do about that.
I also find the old diversion tactics can still work - if I pick the right moment. Jollying her out of it is probably the most successful tool I have - got to pick the right time though and the right way to go about it. Pulling a cross eyes fish face often will do the trick & break the mood 
It's great to know we are not alone.