My 2006 Cts is having some major problems. Going uphill the car is struggling and there is alot of jerking. Also at times on the highway the rpms will drop from 2500 to around 2000 with a jerking motion a few times then go back to normal . It feels like the wheels arent getting any power to them at times. Also while accelerating sometimes there is a rattling sound. No lights are on on the dashboard, and there are no other problems i cant tell other then that. Any ideas?