Did you try some yellow Minispikes? All that cutting and dremelling must be annoying...
At our NORC race in Langenfeld last year, grip was ultra-high. My son kept traction rolling with Minipins and Multibytes, but otherwise the car was dialed. Some slightly to (in the course of the weekend) well worn Minisipikes solved the problem, and the car was perfect! (B-Max4 with Jörn Neumann's Maritime set-up iirc)