heres the low down. Before truck sat up it had a vibration. Started getting more and more serious. Ok decided to put truck up and fix a few things for a couple months. Well, tweaked trans, converter, and cam/valvetrane. When i was puttin it back togther i noticed the rear trans housing bushin went bad. Eat at groove in my personal dshaft. Ordered new bushin and seal. Borrowed JB dshaft with a nice high dollar yoke. Altho, it is a stock dshaft as well. Finally got to driving it and noticed it fixed almost all vibration. Only thing left is a slight one that appears 60-65. Sounds like a rummble type or something. Kinda raddles everything in the cab. Seems like a vibration and rumble from my 3" magnaflow. Probly jack it up and run it or something and look it over. Always chasing something else!

 

Its weird how it only does it around 60-65 mph.. was the driveshaft balanced?

Get the truck on a lift with it running and rev it up through different rpm ranges and see if the exhaust is ok.. i would be checking driveshaft balance though..