Difficult to System Balance the Driveline
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
If after following the Vibration Analysis - Driveline table you were instructed to system balance the driveline and you experienced difficulty in doing so while CAREFULLY following the procedures indicated (the EVA strobe readings seem to keep changing), then the axle differential to which the propeller shaft is attached should be suspected to have internal problems which are being transmitted to the propeller shaft. Refer to Diagnostic Starting Point - Front Drive Axle in Front Drive Axle, or to Diagnostic Starting Point - Rear Drive Axle in Rear Drive Axle, for internal axle diagnostics.