Momentary Pinging/Detonation during rapid throttle application
 

Hello,

I have 1999 318ti with DASC (M44), 3.4" pulley, Stage 3 by NickG

Engine has been running great until recently. Drove to Chicago and filled at Citgo and immediately after the fill-up (premium) the engine started to ping really bad during throttle application.
Went to nearest Autozone and got the octane booster and that helped a lot but not completely. I have now done two fill-ups at COSTCO with premium gas and I am still occasionally getting very quick (1 sec) pinging upon medium quick throttle application. No CEL, no codes. Any ideas how to resolve this? Is this gasoline-related or something else is going on?

Plugs are new and look very nice. Compression is even 205 psi+ on all cylinders. Cleaned MAF, cleaned air filter (K&N), checked for any air leaks.

Thank you.