My DS went through a stage of having completly manic rages. We talked about it and again he couldn't really give reasons (he was 5/6/7). What we did discuss was more appropriate actions he could take if he was getting angry and we came up with the idea of a emergency stop word (i was something like fluffy teddy).
He knew if he just wanted to stop and hug he could use this word. So if he felt he was getting out of conrol and things were getting out of hand he could say this. The deal was I had to stop too and just hug him for a minute then we would talk more calmly about the situation (without over analysing it). Take care that he doesn't see the word as a get out of jail free card to stop you telling him off. More like a time out.
I found he was scared and confused when he got angry, and me shouting at him or getting all excited wasn't helping him calm down.
We went from chairs being flung down the stairs and violent crying to a quite boy who trusted me more and learned when to backdown and as they say "take a telling".
It can be easy to get into a situation when a child feels they have too much control, too many options and too much going on ,and will be overwhelmed by it all, sometimes it is nice to have mummy in control setting boundries and roping them in.
I am not saying this is what was happening but prefives aren't always very good at reasoning things out, discussing options and coming up with solutions.
I am also not keen on rewards that cannot be carried on every time eg put your seatbelt on and get a big sweety. Simpler in for the future if told seatbelt on or I cannot drive the car, as you will get hurt. You can then say the same thing everytime.
Helps to keep the punishments relative to the crime. E.G. Misuse of a toy toy removed from child for the rest of day. Perhaps for kicking teacher no favorite programmes that night and taken to apologise to teacher next day, or even taking time to draw a nice picture to say sorry. Makes them think more about the other person rather than just feeling hard done by themselves.
Sorry I will stop going on now .