I switched to 3 under a few months back and have been loving it. It seems much easier for me to keep tight groups right where I want them at hunting ranges. I still shoot instinctive and have the same anchoring point so the change was easy.
Anyway, I have been getting a slight porpoise in my arrow and I couldn't find out why. It was just slight and my broad heads were still hitting with my FP's. Today I added a tied on nock below the arrow and everything is solved! My arrows are flying perfect now!