It sounds like you have tried everything. But here is what I do for my emotional child when she starts to get into another aggressive phase. It does not end the roller coaster but it does curb it. My DD is 6 now and still has episodes, but they are nothing like the ones she had when she was 4.
The behavior, for her, tends to happen in waves. She's fine for a few days or even three weeks then all the sudden she becomes an aggressive, emotional wreck.
We have not been able to figure out why she gets this way but we suspect it has something to do with her growth or a sleep dysfunction (cranky during growth spurts maybe? My DH has a long history of sleep dysfunction. I'm hoping she didn't inherit it.)
First of all I have to be very strict when I see the signs showing that another episode is about to start. These signs can vary from oversleeping, moody gloomy behavior, complaining about being tired but bouncing off the walls while doing so, refusal to eat (except for sweets and other unhealthy stuff).
Any unacceptable emotional outbursts and she loses computer rights first, then the TV, then her favorite toys get taken up for the day. Though know when to pick your battleground. A bit of grumbling over not wanting to do chores is not good grounds for losing any rights.
We do quiet table activities if I notice her getting hyper. (Crayons, painting, perler beads, clay ect.). She tends to get jumpy and hyper before a breakdown.
Restrict unhealthy foods (one sweet a day before 3:00pm no chips or other unhealthy snacks) and introduce a multi-vitamin. I'm not much for vitamins but when she gets an episode I do give her one a day. Just in case it's lack of essential vitamins causing the problem.
Spend some extra Mom and me time with her playing board games, reading books to each other, baking bread (whatever it is just make sure you are having fun and interacting with him! No watching TV together). With a 4 yr old boy; break out the cars and trains and play with them for an hour.
Force her to play outside for an hour. This gets rid of excess energy and she gets some sun. She doesn't like playing outside. She would rather stay in and play on the computer or read books.
No napping allowed during the day. I know this sounds bad. Some parents force naps because it gives them a break. But you want them to be tired enough for bedtime that they sleep straight through the night.
Lastly, I put her to bed extra early and let her sleep in if she doesn't get up when I do (but be sure to wake her before 10:00am or she will be up all night). This may not be easy if your child is already going to school, preschool, or daycare.
We homeschool, and I'm a stay at home mom so extra sleep time is not an issue for us.
I also spend an hour or more getting ready for bed. We brush our teeth and wash our faces together. Get out PJ's on at the same time. Read a story. Get a bed time snack if necessary (before brushing; non sugary snack, toast and butter or some peppermint tea, no caffine or chocolate or course). This routine calms her down and gets her ready for bed.
Hope this helps, patience is the key.