I found this out the last couple of days, no matter what I did with nock height, I still had a wiggle in my arrows flying down range. I moved my nock down slightly and started nocking my arrow on top. If it wiggles or porpoises (sp?) now, it's because of sloppy form. I can get a clean release like you with 3 under, just can't find a comfortable anchor.
Give nocking on top a try for a few shots and see, it might help, might not, but it did for me. Keeps me from pushing up on the arrow with my middle finger and pushing down as much with my index. For whatever reason, I don't pinch as much with the arrow nocked on top. Keeps me shooting split, instead of fighting to find a anchor 3 under for now.