I just installed a 3" body lift kit(performance acessories) in my 98 TJ. At around 35mph the whole body is shaking a lot. I double checked all the bolts and everything is tight.
Now this is just my opinion, BUT, a 3" lift is to much. I wouldn't go more than 2" on ANY body lift. It make any vehicle to unstable. But, the first thing to check would be your linkages and make sure all the body bolts are tight.[addsig]