Friend asked me at work about his sons f-150. Has a 6" lift about a year old and was a new lift when in stalled. 87 model twin traction beam i guess not gone to look at it and has blocks in the rear. But johnny says at a certian speed especially when slowing down at about 35 it starts to shake and have to hit the brakes to get to a slower mph so its quits quick. Cannot remember how he says it does on accellerating. Let me have some thoughts so i may help them out tomorrow.