Q: “My question is, why does the track get slippery when it gets really hot and how to adapt to it with my tire pressures, as that is really all I can change at the track?”
A: There are a couple of factors at play here.
First, when pavement gets hot, oils come out of the asphalt to the surface, and that can reduce the grip level.
Second, all tires have an ideal temperature range, and it’s possible (likely) that you’re exceeding that range. Street tires, in particular, are not designed to run at higher temperatures – at the kind of temperatures we take them to on the track. So as the track heats up and you do more laps, you’re going beyond what they like best.
You can try running a little less tire pressure when it’s hot. The reason for this is to control what your “hot pressures” are. Same as with temperature, your tires have an ideal pressure range. You set them when cold and they increase when they get hot (the air temperature inside the tire builds, and that increases the pressure). If you start with the same pressure when it’s hot, they will increase beyond their ideal pressure range. So you can try starting them with less pressure. Give that a try and learn what it does.