swaying question

I have a 99' GTP with 88k. Whenever I'm on the highway, the car feels like its swaying back and forth. It gets worse when I'm on snow...like the rear end wants to kick out from underneath me and spin out even at low speeds. The rear wheels are cambered inwards and it feels like they are fighting each other so it takes some effort keeping it straight, but I've noticed that all rear wheels on grand prix's are the same way.

I saw on another thread that an alignment would help but I was told that the springs need to be replaced in the rear. Anyone have this problem?

I had a swaying issue with a different car. It turned to be most of the suspension bushings were worn out, so the entire rearend was loose. It would start to sway at about 50mph, but I could feel it want to pull out from underneath me in turns. The car wasn't worth keeping as the repair was beyond the value of the car. I would have a suspension shop look it, or you could get under there with a flashlight and have a look at the suspension bushings.