Bad Drive Line Vibration

Supershafts
Nothing I have tried works. Last night I took off the drag radials and installed radials from my Dart. A much smaller tire in width and diameter but they are new and just balanced. It did clear up the low speed vibrations, 30mph but nothing changed at the top end. I have adjusted pinion angles and rebalanced the driveshaft. The shaft was made for the car 8 years ago. It has the correct yoke engagement at the tranny. I can pull the new axles and third member from my Dart and try them, but first I will set the pinion to 0 and install the drag radials after I get them balanced and let you know.
Thanks for the help.