So I just bought my '05 CTS with 30k miles on it. Its fine when your driving highway or at an idle... then when you're in trafffic or driving in a residential you notice that the car is hesitating or feeling like its starving for fuel and when you only get up to about 1,500 and come to a complete stop, the engine shakes and won't snap out of it unless u rev it up... almost sounds like an engine knock or a valve tap, but its not. No check engine lights, cadillac says its not showing any codes, I used seafoam in the gas tank. Nothing works. Any ideas? I'm thinking maybe an extremely dirty fuel filter?