Could my almost 4yr old sons behavior and tantrums be atypical, how worried should I really be?

He had started throwing tantrums at 2 yrs old which I knew to expect but by 3 the tantrums were scary. He would scream, kick, punch, bite, scratch and it wouldn't last hours but usually 30 mins to an hour. His pediatrician believed it to be caused by his lack of being able to communicate which is EI team believed to be the case as well. So here we are now his 4th birthday is 3 months away and he continues with violent behavior. Typically if he's repremanded by his father my son almost immediately starts swinging at him and just being completly defiant it seems like my son actually gets enraged. He's a little more behaved with me but i am the working parent and dad stays home with the kids which i know can make the difference. If he's not getting his way he usually will resort to hitting and attacking and even hit his 2yr old sister if he is not able to successfully hit me or his dad! He has gotten some spankings but there is no abuse and we have decided to avoid spanking all together because what if it could be at fault for this behavior or what if my son genuinely can't control himself. Hes generally a sweet, loving boy. He still sleeps in the bed with me and he gets one on one time with me and dad. We are trying not to raise a child that walks all over us but nothing is working. We do live in a stressful environment due to finances and dad suffers from depression and has moods swings but is stable 85% of the time. My son can tell me during his fits that he can't control himself. This is very alarming to me. Could this be more than just bad behavior. His speach BTW has improved and he is able to communicate his wants,needs,likes and dislikes and plays well with children his own age.