I am wondering what the relationship is like with his step parents how do they feel about him what the dynamics are there.What is your relationship here to him seems to be some unanswered problems going on.Is he on any meds that could have an effect on his behavior has he been diagnosed with any disorder? There is always an answer where children are concerned at least I believe there is.
Is there a way to channel this energy somewhere else? Does he have any sports he loves? I'd get him involved in some physical endeavors and try to cut him some slack. Divorce and remarriage is very hard on a kid and they can react badly. This isn't the fault of the parents as they have to live their lives, but being empathetic as to how it affects the kids involved is important during the transitions.
I'd make sure that step dad tries to be more friend like than father like as he like most boys would probably resent that.
It is fair to tell him he can't call names and cuss. But you need to have somewhere for him to go with this anger. Somewhere posative, and I'm thinking that is a sport or art or something. Buy a boxing bag and hang it, let him box. Get him in soccer, let him run and kick the **## out of that ball. And cheer him on the whole time. Keep him in counseling and keep the communication lines open with yourself. Good luck!!