I start getting a vibration at about 45 mph. I lowered the rear 1.5" to see if maybe the drivetrain was too out of angle, but it still vibrates the same. It kind of levels out at about 65mph, or maybe it just vibrates so much that it does not feel so strong. At 45 you can really feel the whole thing vibrate underneath. The steering wheel is fine, so it is not aligement. It could be the diff. I already replaced it about two years ago, but it does not vibrate below 45. Some other people had complained about a similar situation, can anybody tell me what they found.