In the weeks after the race at Infineon, I spoke with other racers about my experience with my tires lack of grip. Lots of speculation. Most people thought it was b/c I had so many heat cycles on them. It was an obvious conclusion - but it was not correct. Testing the tread with a durometer showed that the tires were actually still nice and soft and not hardened from heat cycles.
I kept on exploring and finally figured it out.
At the last race, I had decided to "flip" the tires to even out wear patterns. Flipping the tires refers to dismounting them and remounting them so that the inside tread is now on the outside. This enables you to get a little more life out of the tire and saves money.
Turns out when you "flip" a tire, you need to put at least one session on them. Otherwise the tires do not grip. Major lesson learned....
In retrospect, I'm not sure if this actually saved me any money. It cost me a few $ to flip the tires and the car didn't have any grip, ruining a race weekend.
When "Flipping Tires", plan on doing a session or two on them so that the tread grips again.