[racer_d]

I guess the real first step is confirming what improvements are allowed for NASA TTC class (or any other groups you would use the car with) before doing anything.

Sticky tires will help immensly, as will reducing tire stagger front/rear. Not sure MPSCs are the best out there but certainly a safe place to start. I would the worthy tires in the following manner, best to worst: Hoosiers, then Khumo V710s, then Victoracers, then RA1/R888 then MPSCs.

the GT3 front sway bar is a popular upgrade for reducing understeer.

5-7mm spacers up front is also helpful to dial out understeer

Alignment is critical. Using factory components, you will never get "enough" negative front camber for use with the tires mentioned above. Most can get between -1.5 and -1.9 degrees, beyond that you need camber plates and/or GT3 Cup lower control arms. Not sure how legal these would be for your class.

IMHO, PSS9s are too much of a compromise (catering to street and track compliance is not easy. They are a good upgrade, but still a compromise). If rules allow, I would search out something more "race" oriented.