I went threw a driveline balance issue with my 4runner. I have a few questions[
1. are you sure its a driveline issue sometimes front suspension and tire balance can feel like driveline.
2. have you tried the drive line in different positions on the differential yoke.
3. is the driveline a original driveline with a rubber liner
One thing I have found to help and Isolate the problem is to put your 4runner drive wheels on jack stands and chock wheels as needed if 4wd it is best to put all wheels on jack stands. When this is done start the 4runner put trans in D slowly bring speed up to vibration speed. If you tires are balanced and you feel a vibration then it is the drive line. You can trying to move the drive line in each spot on the yoke.