I've looked at a lot of posts but haven't found anything that covers my problem. I'm getting an intermittent driveline vibration at 35 mph and up. It feels like an out of balance wheel but much worse. It gets worse the faster I go. Going into neutral doesn't help. It doesn't happen all the time - maybe a couple of times a month. Stopping for awhile cures it, until the next time. I thought of IWE problems but didn't see any similar problems posted. I thought of LS rear clutch chatter but it happens when driving in a straight line. The last time it happened, this morning, I made hard left to turn around and head for my dealer and that cured it. My truck is a 2006 with 42,000 miles; 5.4L,, auto trans, manual 4WD. Anyone have any ideas?

 

I had this issue. Really felt it through the gas peddle. In my case it was the front u joint

 

Parking brake?
Drive shaft?
U joints?