Hi Rev,
You really need to change your tire combination. If you run magentas up front you really need to be running pinks on the back. Magenta's are WAY to aggressive. For Stock the most consistent set up I find is white on the back and purple on the front. I can give you a set of purple fronts, they are used but in fine condition, I don't have any spare white rears but greys work well also, probably better on a t-bar car. When you get purples on the front, sauce them 2/3 to 3/4. I ran purple / white last time in stock and got within .4 of my best mod lap time with a sucky stock motor.
JohnB,
Try less castor on the front, you could also try a sfter center spring.
Chris.