What kind of goodyears? and how much mileage you got? And is your driving a more aggressive routine or is it normal?
also if your tail end is kicking out I suggest checking your owners manual and seeing if you can put more weight back there, safely, assuming you could without compromising usage, because if you had some weight over the rear suspension, 80lb sand bag for example, and your car has anything ot say about PSI when towing or hauling(FOr 1 sand bag I would personally add a pound or 2 to the tires) because the weight over a more "asserted" contact patch would theroetically and hopefully mean your car is less prone to that. and for slowing down it will increase stop distance because of weight added but it should be easily balanced by the rear being able to brake more.
If your car is NOT new to you, then my suggestion otherwise is to have your throttle position sensor/throttle body "relearned" and your transmission adaptive shift learning to be reset as to allow your driving style to be learned. someone heavy on teh throttle, like me, would make a awd system in your car likely bias the rear if not just more "into" it as to not hesitate, sag, or feel sluggish. But you may be less spirited. The throttle thing is thesame concept. I just relearned the throttle and relearned the power steering on my gmas Jeep(jeep obv, but i suspect similar things exist on buickregal) Because idle was dipping too low and not much assist atlow speeds or stopped and the thing was like 3 seconds from stop to actual go from hitting the go go lever with my go-go brick.