OK, first off you can restrain him at 3yr old no matter how strong you think he is. You just need to be shown how to do it safely for you and him. Maybe ask his pediatrician to show you how? I had to have someone show me how and it really helped keep everyone from getting thrashed on. I think this is a skill every parent should be shown right after they receive the diagnosis.
About ABA, ABA is Applied Behavior Analysis. It is a type of behavior modification therapy and if used consistently with 110% effort on your part it will be successful to some degree. It takes time, a lot of time and commitment on your part to think differently and act differently towards your child's behaviors. Some things are simple and some things require more trial and error and time. It has been successful in many ways in my family. Basically you work one on one either in office or intensive in home (depends what you can afford and what you can get in to quicker). Unwanted behaviors are prioritized and spotlighted one by one. You chip away at the unwanted behaviors little by little by isolating and analyzing the behavior and then coming up with an action plan just for that behavior. Each ABA therapy for each child is unique because each child is unique. You will need to make sure you trust and feel comfortable with your ABA therapist. For example in our ABA therapy I have learned alternate ways to discipline my child that do not include time outs since time outs do not work for us either. I have also had to relearn what I thought about discipline in that many ABA therapies are based on rewarding positive behaviors and ignoring or redirecting negative ones.

Time outs do not work and not does raising your voice to an ASD child. If you can reason with them in a calm manner and explain why that is not tolerated that would work best. If that is not possible you need behavior modification through ABA and possibly meds to get the child under control. If that does not work you may need to consider more extensive methods and schooling. You have to get this under control before the child is so strong you cannot handle them and they either hurt themselves or someone else. I know a lot of people cannot accept that they cannot handle things and do not want professionals or out of home treatment but the truth is that delaying treatment in severe cases helps no one most of all the child. As they get older it will get worse so you need to deal with it now

I think a lot of his behavior issues are from his seemingly inexhaustible energy. I thought I was hyper as a child, but boy, he puts me to shame. However, I will contact the behavior specialist and speak with him about ABA/behavior modification therapy again.

This is very common for the child to act differently when they are away from home because they are less comfortable. Even with ASD your child will still test his boundaries like every child would. The key is to try to figure out what the causes are so you can try to stop them. It may take trial and error before you find something that will work. ABA is a big part of that so starting it will help

You need to figure out WHY the function of the behavior before you can find anything effective to stop it. In home behavioral therapy should help. The website behavior doctor is a good resource for FBA (functional behavioral assessment) as well as school personal.