This may already be out there but just in case it’s not… I just had the Rough Country 6inch lift installed on my 1999 K2500 Crew Cab Short Bed. I bought the kit from Rough Country directly. Once installed I had a violent vibration at initial take off. It turns out the kit is not for crew cab short beds (Rough Country does not designate short / long bed, however my short bed has the factory 454.). It’s for crew cab long beds, extended cab long bed. So after many calls to Rough Country Customer Service they were nice but unable to help, My guy did the math and with some trial and error, cut the cross member supporting the carrier barring in the rear and lowered it by 2 inches. This corrected the driveline angle and Completely eliminated the vibration at take off. Hope this helps someone else who may have this problem.