Driveline vibration

Not the wheels.. thought I got it figured out. Drilled out my old steel wheels for 5/8 studs, went on the freeway, same vibration at 70. Anybody know something on critical speeds. 5th gear is .68 rear gear is 4:30 and tire size is 26. Am I spinning drive shaft too fast. 3.5 inch steel can’t recall how long..
Also like to note my drive line angles are about the same, within half degree how the old 8-3/4 was and that didn’t vibrate.