I can't say what to do or what's going to make it better but, I think that you need to take away the TV, some agression could be learned from watching tv. Also, every day take him to the park or to do a physical activity, sometimes kids get tooo wound up and get agitated when they are tired, its a way to fight off sleep. Kids thrive on routine, if he knows what's going to happen next he'll follow suit, but if he doesn't know what is going to happen next then he wont know what to do and get bored or get agitated.
I think that the best way to get kids to behave is to get them really tired by doing something physical and fun everyday and then going home for a good nap.
He's also at a tough age. I realy thought 3 was much harder than 2. They test and test and test. Your job is to remain calm and guide. Sounds like you are trying hard to do that.
I don't know if your son has a medical condition or not---------- it is really hard to say with little ones your sons age. They are all so different and many kids really do act like wild maniacs without an ounce of self control that grow up to be just fine.
I have two boys. They did a lot of the same things as little guys. They are now 6 and 5. My 6 year old does have a developmental delay called sensory ingegration disorder. This has nothing to do with IQ as he is quite smart but his nervous system is over active. He processes things differently than others. So we do a lot of work to "slow" his nervous system down. I'm going to tell you some things you can do that we learned in occupational therapy to calm a child and help them self soothe, behave and listen better.
One of the biggest things you can do is physical activity. I can't say enough about this. We go to parks and run, climb the structures, jump off of them, roll down hills and run back up, and swing. Every day. It's so important for the nervous system and can be the key to better behavior. If you already do a lot of that stuff, do more. You can google "heavy work" which is the occupational therapy term for muscle work that soothes a child. Pushing a laundry basket with some items to give it weight across the floor, doing a 'wheelbarrow" walk, crab walk, bear walk, carrying a bag with some books in it as a "favor" (make things seem fun), swimming, etc. These things all calm internally a child.
If he is getting into things that are just decoration--------- do yourself a favor and just put them up. I went through this phase of "they will LISTEN to me and not touch my "pretties" (as we called them)". Well, they didn't but I had to constantly keep after them and it was a hassle. I put the stuff up and just recently got it back out. Some may not agree with me on that--------- but I saved myself a headache with that. It was worth it. If it is things that aren't safe-------- cabinet locks work. Door things that they can't turn and open the door themselves are an option. Stay calm and set up the boundaries as you go. Everything can't be a no and everything can't be "hands off". I had a cabinet in my kitchen that had old pots and pans and lids in and my kids had that as "their" cabinet. They could play in that one. They never even tried to open another one. And honestly, a child of that age requires a LOT of supervision. You follow them around a lot now but it pays off later.
"SOS for Parents" by Lynn Clark is a good book and goes through proper time out technique. I also put something special into time out--------- my son's blankie, for example (HAS to have his blankie). You always have to be consistent though and follow through. Don't just throw out threats-------- have a warning and then something that will follow and follow through or he won't take you seriously.
It is hard work but stay calm-------- you'll make it through. And don't think I don't know how bad it can be-------- my sensory kid was very hard to manage. He's 6 now and it is so much better. So stay calm and TEACH him now and it will pay off. good luck