My son is 3 1/2. When an authority figure (teacher, parent, etc.) asks him or tells him to do something, he gets bent out of shape and throws huge tantrums. He flies off the handle and screams, kicks, hits, pinches and throws things. He's to the point where they are going to boot him out of preschool. The teachers asked him the other day not to climb up the slide backwards. He wouldn't listen. When she removed him, he hit her in the face, knocking off her glasses. He's kicked, hit and has thrown things at teachers. Everything is fine if it's his idea. If you ask him to do something he doesn't want to do, there's a problem. We've done time outs, toy time outs, and gently holding him while he's trying to hit us.

I do not spank my child, even though sometimes I feel it would do him a world of good (even though it really won't).

My Mother spoils him to pieces. She jumps at his every whim and never gives him any alone playtime. She also cooks to order what he wants when he is at her house if he doesn't want to eat what everyone else is eating. We do not do that at my house. I ask her not to spoil him and she says "I do not know what you're talking about".

I am going through a divorce now and it is an adjustment period for all of us. This behavior started waaay before anything was brewing at home.

Is there a good correction technique to use?

We do not have any health insurance, so going for an eval. is out.

He does not eat dairy or junk food.

Oh! My heart goes out to you. Have you tried to get away. Just you and him in the house for a bit. No friends or family. I had to do this with my 3yo. I only had 3 hour for two days. We talked played, and read books about the behavior the needed changed. We used my little pony's and acted out a sit. and we played diferent rolls. On the second day we did it again and I really pushed the words she needed to say to get through the problem ie. "I am not happy about this!" "This is not in my master plan" ( my dd's fav.) and the dreded "But why must I" I like to add the must I cuz then the kid is saying that they must and it sounds so cute coming out if little kids. That is just my thing. We are do for another session.
As for Eval. I would call around. Youmight find a program that is free from the state or a Univ.
Gee, good luck.

hard situation. I like the role playing idea with the toys. I'm sorry you are having to go through this. He might be sensitive to something else he is eating or "not" eating enough of something. Does he nap? How does he sleep?

Maybe some Chamomilla 30C could help him for a bit.