Well after I got my UCAs/LCAs, Coil Overs, CC Plates, Illumina shocks/struts installed I allways had a very slight vibration at about 80-100kmh (highway speeds) in at low rpms when just light on the throttle. I allways thought it was just the way it was going to be with the UCAs/LCAs since it was very mild. Well I was going thru my old parts and moving them when I saw this big metal hunk "wtf is this" I think...then remembered when I got the suspension done the guy removed the 'wishbone?' is it called the counterweight over the rear end. He removed it becuse most ppl do with stangs, its like 15lb right there. Anyways put that back on and my vibration is gone. Its actually a metal weight with rubber isolators in it, so it absorbs the vibration from the rear end. Thought id share incase anyone else has a vibration it takes like 10 seconds to look to see if you got the counterweight on your rear end.