Reducing toe-in will not help you, instead it will make it worse (increase off-throttle oversteer) . Leave it 3 degrees.
As for the diffs: try running thinner oil at the rear diff or/and thicker oil at the front diff. As a general rule, when the rear end
of the car doesnt have traction, we try to "borrow" some traction from the front (and vice versa).
Have a look on the setup book, it has nice info at the end with setup solutions to every problem (oversteer, understeer)
and when it appears (corner entry, middle, exit). If not available under 733 section, i am sure is available under 720 section. Make one change at a time and see how it works. Try first the changes with the highest priority (1,2,3, ..etc).
Good luck