I completely sympathise. I have my own little threenager too!
Of course all 3 year olds are different and some are more strong minded than others.
In my own experience having a clear routine, being strict and consistent are the key to a calm life. Routine for us means that I have to be firm and have set times for getting up, having breakfast, what the options for breakfast are, meal times, nap times, bathtime, bed time etc. Generally, the more we deviate from standard routine, the worse his behaviour. Not saying we don't have nice days out, but if doing something new and exciting I'll try and keep as much else as normal as possible.
I'm no toddler expert, but knowing what the 'rules' are, where the boundaries are, appear to be really important at the moment. So this means being really strict whenever establishing a new rule. E.g. DS doesn't go in his buggy so much now so walking around car parks, into town, crossing roads etc is pretty new to him. I enforce the rule that he HAS to hold my or DH hand. If he doesn't we don't go any further and might even go back to the car until he agrees to hold hands.
Also being clear and consistant. I don't have a conversation if I'm telling him what he needs to do. It's a simple - 'Stop' 'Stop now!' I also am very conscious of not making empty threats. If I offer a choice I have to be willing to follow through with both options. Never make a threat that you won't enforce.
Oh and food is also a big trigger factor for behaviour for my DS. If he has squash with artificial stuff in, chocolate, sweet stuff... most processed foods, he'll turn bonkers and won't listen to a word I say! But if he's hungry he'll also get very emotional!
It sounds like you've tried lots of things OP. I'd say come up with a plan and just stick to it. Don't expect quick results. Keep firm to your rules for at least 3 or 4 days before changing things or giving up on one tactic. You don't want to confuse him. Good luck!