Terrible 2¾'s

Lucas is spitting, kicking, biting and not being the sweet loving little boy he was a few short months ago. I hear a lot of "Give me" or "I need". No please or thank you - despite us drilling the manners into his brain they seem to leak out. He is prone to sudden bouts of deafness. He is completely non responsive to request for assistance or reprimand for hurting his brother. What am I doing wrong? I don't yell a whole lot, I don't spank, I use positive reinforcements in accordance with the famous Positive Discipline Book that everyone swears by. Yes I do own the book and yes it is a good book, the ideas put forth make sense and seem as if they would work. But it isn't working. At the risk of sounding self-righteous, I think this is just his age. I don't think I'm doing a whole lot "wrong". But I guess I'll know if I've screwed up in about 20 years from now. That is reassuring.

This parenting stuff is hard.