Evening boys and girls.

I've had my car tuned for a while, and it seems that up in the high end of the RPM scale (4000+), the car is pulling back timing from possible knock. The car is maxed out of boost at 16psi, I'm putting it down to potential spark blow out. Has anyone with the stock plugs tuned, gapped the plugs closer with good results?

We have eased timing from the first signs of timing being pulled, but it's continuing to pull.