I'm guessing that you know about cleaning the tires too, so try full sauce
on the rear and if possible try hardening up that rear stablizer you got on there.
You could try removing it all together. Just make one move at a time incase
whatever you do makes the handling worse. You could go back one step
and try something else.
In addition. Try picking the brains of one of the top mini drivers at your track
Have him try driving your far to see maybe its something in the way your handling
Or maybe in your setup on your controller.