The dealer ask me if vibration was only when just beginning to drive before warm-up. The car was very new and I didn't know answer. Now I know, the answer is "no". It happens when car is cold and when it has been driven for awhile. He suggested it may be tire(s) with a flat spot or possibly the transmission. The vibration starts about 45 mph and slowly builds to about 55 mph, then begins to lessen so it is almost gone around 60 - 65 mph.My wife drives the car most of the time and she says a few times she has felt a hesitation when she pressed on the gas peddle to start from a full stop or when she presses the gas peddle to accelerate for passing.Yesterday she said it feels like she must press the gas peddle more to achieve the same acceleration she got in the past with less peddle pressure, but she's not sure as it's a new car and she may be remembering her old car.We have no other problems with the car except the trunk lid needed to be painted after purchase.