First, welcome to GCM.
Second
2 Sounds like a tough situation where your son has more playing into his behaviors than what the trigger at the moment is. 45+ minutes of anger plus a history of multiple meltdowns in one day as a regular thing in past years, and he is recently officially adopted. That is a lot of factors that point to him needed some extra help. It also sounds like he is desperately in need of knowing that you will love him forever no matter what even if he doesn't realize at such a young age that that is what he is
testing.
I hope you find support here and a way to help your son. 6 is hard enough and when there is more going on that challenges even tougher.