Get a different rear sway bar - by installing a much larger one you have induced oversteer.

What bar exactly is this and how was it installed? Have you though about going back to the stock bar? Tossing a bunch of parts on there without knowing exactly how they are going to affect the handling is never a good idea. Do one thing at a time so you can see what happens - good or bad, then the next part. I've only got shocks and struts and it handles well enough that I don't even think I will touch the sways.