2004 Chrysler Pacifica Vibration Acts Unbalanced Tires

Where do you feel the vibration, in the steering or the seat?

Well, . . . have them balanced. With no other details or information, a tire could be out-of-balance, could have a broken belt, a bent wheel, a cv joint could be worn, or a steering or suspension part could be worn. Professionals narrow down what to look for by knowing what speeds or loads it occurs at, if turning or accelerating affects it, and whether the vibration is felt in the seat, steering wheel, or whole car. You didn't supply any of that information.