The problem with the St is it has a very poor clutch as standard and when you start to tune them the clutch can't handle the torque, even just a stage 1 remap can cause it to slip. It can slip in just the winter as with the colder temperatures the air going in is colder and the intercooler is working better because of the colder airflow which both result more power and torque thus causing the clutch to slip at certain times of the year when the air is at its coldest.