Need some tuning help from some of you Professionals.

[CDeutsch]

The ECU is bumping up your timing with the RPMs. Maybe when you hit 5200 it's too much. How much timing have you tried pulling? You could also try 100 octane and see if it goes away. At least then you'd know if it's real.

What happens if you slowly take it up to say 5500-6000 so you don't get knock and then go WOT? That might help rule out harmonics.