If it happens from high speed it could be aero balance, so add some rear wing if you have aero fitted.
Ride height differences front and rear can change the balance too (either due to aero effects or geometry). On some non-aero cars I've tested, a higher rear makes a sharper turn in, so in your case you might want to lower the rear, but check it both ways as it's not always worked in every car I've tried.
LSD decel is useful, add more to help stability, also bias brake balance to the front to prevent rears locking up .
Using less toe out (or more toe in) will add stability particularly in the first tiny steering corrections you make.
If you've weight reduced the car a lot, I think the weight distribution can alter so you could try adding ballast.
Softer springs and dampers, particularly rear springs and rear extension damp, can slow down the load transfer off the rear tyres. The car may still be tricky but it'll happen slower so can give you time to catch the misbehaviour.
If you want to post the setup on a problem car I'd be happy to test drive it (if I own one!)
