Due the Strano springs!!! period Ive heard nothing but bad things about about Eibach springs for Fbodys. Here is a pic of my Stranos with Koni adjustable shocks and struts

 

i have had the eibach on about a year now and not any problems, there much better than stock . people say they sag on rear, i dont know about this, in my opinion they are just low, lower than quoted. Mine has dropped like 2 inch at rear and 1.5 at front, but they have always been the same since they settled in. The pro kit what i have is more a middle range, not too hard but good handling. I know stranos spring rates are up from eibach but its all down to personal choice.