3000TT pistons, and you keep the quench areas - quite important to do so esp. if boosted. I've seen gasket spacers make detonation worse because you lose the quench and resulting turbulence and dead spots where it can't detonate.

Look at the plugs for bright specks of what looks like aluminum spatters - usually quite small. Those are the sure sign of detonation. The unburnt air layer next to the metal gets blasted away from the suface by the shock wave of the det, and lets the combustion heat actually touch the surface of the piston and combustion chamber instead of being isolated by that molecules thick layer that won't light because of the nearby heat conduction that keeps it below the ignition point (surface quenching), and little flecks of molten aluminum go flying around.