05 Maxx vibration at hwy speed

Purchased a 05 Malibu Maxx LT last Sunday. Had to turn around on interstate after 20 miles and return it because of full vehicle vibration. Dealership offered to upgrade us to fully loaded 05 LT at same price. We agreed and left the dealers lot. This 05 LT with 5 miles on OD had same problem but to a lesser degree!!. Returned car a couple days later to have wheels rebalanced. Service consultant said car still has vibration and that GM recommends that I drive car for 1000 miles and bring it back if problem still exists. Has anyone had a similar problem? Can a car develope this kind of problem from sitting on a lot for close to a year? I do love this car and hope things will work out.

Purchased a 05 Malibu Maxx LT last Sunday. Had to turn around on interstate after 20 miles and return it because of full vehicle vibration. Dealership offered to upgrade us to fully loaded 05 LT at same price. We agreed and left the dealers lot. This 05 LT with 5 miles on OD had same problem but to a lesser degree!!. Returned car a couple days later to have wheels rebalanced. Service consultant said car still has vibration and that GM recommends that I drive car for 1000 miles and bring it back if problem still exists. Has anyone had a similar problem? Can a car develope this kind of problem from sitting on a lot for close to a year? I do love this car and hope things will work out.
I would request an exact reason for this vibration, like are the tries flat spotted after sitting for a year? Then ask what was expected to happen in 1k miles? In the future don't buy a vehicle that has sat for a year unused, this is worse than driving for a year.

If they really think it is the tires, then just temporarily trade them with wheels from an 06 car, take it on a drive and find out. If it is the tires, I am sure GM or dealer will replace them.

Keith