I'll jump in a different direction than coil packs and vacuum leaks. I had misfires and ultimately a CEL that my son said happened when he got above 3K RPM starting about a month ago. After looking at codes / CEL and determining it was misfires, clearing the code / CEL, replacing obviously bad check valves, having it come back most times once above 3K RPM, I decided to start digging deeper. I was nosing around all the vacuum lines and finding nothing when I decided that since I had my shopvac out, to vacuum the debris in the cowl area to keep the drains clean (I know, what does that have to do with anything) and for some reason my eyes rested on my air cleaner with a K&N sticker on it, and wondered "hmmm, wonder what my air filter looks like". I removed it and oh my; it was probably over 50% clogged. I cleaned it, reoiled it, and reinstalled. Haven't had a misfire since and even invited my son to drive the car a little aggressively at times to try and induce them.
Long way of saying check your air filter...
02 sport quattro with 205K; killed by a 4x4). Now an 03 1.8t sport quattro with 101K