Is the alignment definitely right? Where was it done, and on what equipment? How long ago was it done, and has anything been fitted/replaced under there since?
How much torque are you running? And is it a big lump of it at 3-3.5k, or a smoother curve? Do you have a graph of your current map?
I personally found PSS were excellent in the bends. The car still behaved like a front driver should, but they reduced understeer massively over the Kumhos that were on the previous wheels. Fantastic tyres.
I did find they'd struggle with straight line grip once they were down close to 3mm or so. Replacing them with new PS4s improved that considerably. I'm running 350lb/ft+ and still get a bit of slip in 3rd at full throttle around peak torque, but only really if it's wet or colder than around 7-8 degrees.
I won't even entertain the idea of winter tyres when in all conditions except near enough freezing a good summer tyre like the PS4 outperforms them by miles.
Last possibility... Do you think the car might ever have been in a bump?