I'm with 1500Sleeper if it is ballanced it should run true. There are pleanty of trucks and cars out there with steel drive shafts and low gears with no vibrations. Hell the cars from the 60s came with 4.11 gears steel drive shafts and smooth as hell. Check both of your u jounts the should move back and forth witn no binding. Check your drive line angle ( this is very important ). Aheck this out! http://www.drivetrain.com/driveline_angle_problem.html