i just installed a 6" suspension lift in my 96 f150 and i''m getting a bad vibration that happens between 40kph and 60kph i dont know if its the tire alignment i tried setting it as close as i could with a tape measure and the pinion angle is almost in a direct line with the driveshaft its just a couple degrees less ...i used the wedges that were supplied by rough country. any ideas as to what the vibration is would be helpful. it shouldn't be anything in the front end cause i have manual hubs and they're unlocked.