Did you ever swap the tires to a good all season or other tire for the cooler temps? obviously it is warming up now so tires shouldn't come into play as much... edit just saw your response
secondly, this to me sounds like it could be a defective wheel speed sensor (or some sensor relating to traction/stability most likely a wheel speed sensor) where the sensor is sending erroneous data making the car think a tire is slipping more than it is causing traction to kick in and kill the power far more dramatically. However, if you are accelerating normally and the back end is slipping/sliding swinging out on regular turns, then something is off, either defective tires/ LSD (Limited Slip Differential) like they think it is, /or really messed up alignment/damaged suspension. On our AWD with michelin pilot sport All Season 4 tires, even in the cold and wet i can pretty much floor it out of corners/intersections and only then will the tail end step out some, coming from a RWD bmw, this car feels like you can drive it like in the dry when in the wet and cold with the awd and good tires.