Yeah, something is going on. It fell flat on its face at exactly 5500rpm. The HP curve was still increasing when that happen and from earlier dyno sessions I know this engine will easily do 6000.
The #4 actually has a slight mist of oil on it from what I can tell , it is not matte black like pure soot but ever so slightly "moist".
I'll roll up my sleeves, bust my knuckles, and yank the other 7 plugs out and have a look . I'll post pics for you to see.
What also worries me is what Nightmist66 said, vacuum or exhaust leak. I can't find any evidence of an exhaust leak from the heads and the O2 sensors are in the collectors before the joint. There is only one vacuum line, going from the throttle body to the MAP sensor, and it looks good. Line is new, fittings are new.