Drive Shaft vibration on 2010 Coachman Freelander

Hello and thanks for the responses. All underneath is brand new and clean with no damage or missing weights. The GM dealer stated the angles of the driveline are probably the issue. The rv dealer sent the driveline out to be balanced and winnebago will not authorize the GM dealer to perform the repair. If I am right, this is six weeks now and will be next week before they get the driveline back to imstall and test.