2008 Chevrolet Impala tires problems

I bought a brand new impala, year 2008. After approximately 10k miles I experienced a vibration in the rear when braking. When I brought the car to radley chevrolet in fredericksburg, they told me that the rotors were warped and it was my fault and not covered by warranty. They said that the lug nut torque was not correct and uneven. I never touched the lug nuts or rotated the tires as the torque issue was rear only and tread wear proved there had been no rotation.

When I stop at a light or just come to a complete stop my car doesnt seem to want to go when I step on the gas. All of a sudden it shudders and jerks forward. Very dangerous when the roads are slippery! This happened just after the warranty expired, but I am guessing that it only had about 46,000 miles on the car. My dealer said I would have to pay for them to look at the car, could run into alot of money, or wait for the check engine light to come on.