Apologies carborush was having a bad day yesterday.
Are the other guys at your track not willing to share setups? Even if they won't tell you what oil to run in the shocks, then you should be able to see the rest of their settings. I would start there.
Alternatively, are you running a hotter motor than the rest? It may be the extra punch you are getting out of turns compared to them that's causing the back end to break loose.
There's some info on diff settings on this thread:
http://www.oople.com/forums/showthre...t=diff+setting