D.,
Have you talked to his teachers to see if anything new is going on at school other than him hitting and saying no?
Kids do go through testing phases on and off throughout their years, but sometimes they're not just being awful to test, sometimes it is just how they handle stress of some sort. My son (10) is such a great kid, but if he lacks some personal attention, after a while he will be a pain and act up, pick fights with his brothers, etc. My oldest son (13) always felt misunderstood and constantly acted out (he is an overly sensitive child, so this didn't help since he always was feeling wronged). When he was in preschool and I asked about his day, his answers were always that he had no time out or that he did. I asked the teacher if he spent a lot of time in time out and she said no. Apparently, the time(s) that he did, was enough that he based his day on it. I made a huge mistake with him thinking things would pass, but they only got worse. He was an extremely sweet kid and then get completely angry in no time. It took 13 years to get him to stop "fighting the world" and take control of his emotions.
My point is, spend a little extra time with your son in the next week or so. Talk about school and friends. Maybe something will come up. You want to be an advocate for your son and find out if there is anything bothering him that is causing this. You also don't want to baby him and let him get by with things. Stay firm on discipline when he has acted out, but in his good moments, try and spend time together and talk. He's a boy and only 3 so he's not going to have long conversations, but you can ask him about things while he plays with toys (like you mentioned role playing). Most importantly, stay patient. I could see a difference in most of my kids in no time whenever I dealt with an issue, but as I said before, my oldest son took 13 years of my patience. Since he turned 13 he has matured so much and is such an easier kid to live with (odd, I know, since you always hear of horror stories with teens, but so far my 3 teens are easier than toddlerhood was).