Setup help cyclone

[samd]

I have a moorespeed cyclone and am running a front roll bar and a 3deg rear toe in. Car turns in to bends nice but looses rear end grip from the middle of the corner to the end.
I dont know what springs I am running it just as the car came second hand.
I was told to put some spacers under the rear hinge pin blocks will this help?
Last option was just to chuck some lead on the rear. Can anyone give me some advice? Ta SAM