I think it has something to do with the alignment settings from the factory. Our Trailblazer isn't as bad as what your describing, but it could be better. I suspect it is the toe setting, either too much toe in or toe out. Either one can cause wandering or a strange over center feeling. I also turn sport mode on every time I drive because I like the steering and shifting better. It's also a good idea to check your tire pressure as the problem will become more pronounced as the tires pressure goes higher. I run mine at 38psi (cold). You could always ask the dealership to check your alignment to make sure it's within spec.