Tons of vibration threads out there, but none quite like this. My rig receives a nasty vibration around 66mph. Up to 65 and past 67, everything is silky smooth. The vibration is there when I'm on the gas and when I coast, slowing down to 66. It's nasty too. Damn near the whole cab wants to shake off the frame. Everything is crazy smooth at any other speed. I rotated the rear axle a while back to achieve a perfect drive-line angle, using a custom CV shaft from Jesse, so there's no issue there. It almost feels as though it may be coming from the engine itself. My tires are well balanced, both with weights and dyna beads (very smooth BTW). Not really sure where to look for this one; possibly engine mounts? I hate to think it might be gearing, either in the auto tranny and or tcase. Any suggestions would be helpful. TIA!
