had it installed today at 4wheelparts, what it does is, when you lift yur truck yur drivelines are at a wierd angle, making a vibration at slow speeds and at highway speed, anyhow this corrects it, took bout 30 minutes and 75 bucks but the truck feels like its stock again. it's nice the power feels alott smoother too! anyone who lifts with an auto trans needs to do it!