Carissa, Sorry to hear you are having so many problems. Although, it makes me feel pretty good. We have had to have one door seal replaced and that is the only problem so far at 12,000 miles. We picked up our 6GT in march of 05.
First, I would recommend taking the car to another dealer.Also could contact GM customer service. If not satisfied there,try taking the car to an independent tire/repair facility. A good place that repairs cars and sells brand name tires. I am talking like a Goodyear franchise.
Explain the problem of the shake and pulling to them. I would agree with Bob and otcpharm that the tires are at fault.
I would think you would be much happier with the car if it didn't shake or pull.
Sorry for the long winded answer. That is my opinion. I am a mechanic, have been for a long time, 25 years or so, but, I did not stay at Holiday Inn Express last night.