I have a similar story. My son is 7. I found this site about a year ago. After many recommendations I read The Explosive Child. It's wonderful!! I recently completed a 12-hour course on the method. I know parenting a challenging child can be so exhausting. You are not alone anymore. There is so much support on this site.
Kids do well when they can. He is lacking skills that are making it difficult to behave. He is not manipulative, attention seeking, rude, etc. he wants to be good just as much as you want him to be. He is not behaving this way because you are not consistent, you are too passive, too strict, etc. He is not a brat and you are not a bad patent...don't ever let that get into your head.
Feel free to message me if you would like a copy if the course materials.