3.2L V6 2009 A4 quattro

I have a misfire in cylinder 6 (back right when looking under hood at firewall). I'm wondering if anyone has an idea on the cause based on one curious fact: It only occurs when I accelerate modestly when already going 50+ mph. Once I park, turn off engine, and turn back on, no misfire. Doesn't occur in any other driving circumstance.

I replaced all 6 spark plugs, 6 ignition coils, cleared the code, and it still occurs only when accelerating from over 50mph. It also doesn't misfire every time I do that.

My next thought was fuel injector (which I can't replace myself). Does that specific event that causes it to occur ring any bells? Thanks in advance