Shev - do you have long rear wheel studs with open lug nuts on you car? I need to find someone with a set of 275 60 15 MT DR's on wheels that have open lug nuts that I can try on my car a couple times to see if it fixes the sideways problem. Just checking. If not, maybe Dave has a set of slicks?
Call Dave on those, he has slicks and he runs the long wheel studs with open wheel-nuts as well. Is the swaying bad on the top end or all the way through? Also, are you running 8" wheels or 10" wide?