Tire Sidewall problems of the 2010 Toyota Corolla

I purchased a 2010 Toyota Corolla s on 11-7-2009. On the test drive I complained to the salesman that the steering felt strange. It seemed to have a center spot and then any left or right turn would cause a minor pull either direction as if the steering turned on. The salesman said it was the electric steering on all the new cars. That was a slow speed test drive. After the purchase I got on the interstate and was shocked to feel the steering feel as if I were going around a semi tractor trailer rig and being pushed around by the wind, but yet I was not near a vehicle. It seemed like loose steering or tire squirm. When I got back from my trip I took it to the local Toyota service center and asked if there is an adjustment on the power steering or if there is an issue with the tires. To both questions my service advisor said no. On another trip on the interstate, it all of a sudden started acting like it was going to fish tail swinging back and forth, like I was ridding on balloon tires, or without sidewalls. I quickly slowed down. In cross winds or going around a semi it is worse. At my 5,000 service, I asked if there are any steering or tire issues, and my advisor still said no, but part of the service was to rotate the tires, and this has seemed to lessen the squirm. I now have 7,000 miles on my 2010 Toyota Corolla s.