I have a 2005 F-250 no mods to the drivetrain or engine except a K&N intake. My cab vibrates pretty significantly between 45 and 70mph and only if the revs are above 1500. Before 45 and after 70 there is no vibration and if I'm coasting down a hill or to a stop there is no vibration. My intital thoughts were bent driveshaft, but I crawled under there and there are no impact marks. The next step I would assume is to get the drive shaft rebalanced but I was wondering before if there were any other options or if I was approaching this from the wrong angle. Any help would be appreciated!