I have been researching and trying to get some ideas on what avenue to pursue to diagnose this, but after a lot of reading I am not finding this exact problem. Hopefully someone has experienced the same issue and has found a resolution. I have a 2015 F250 Super Duty gas engine with 115k miles and for some time have had a problem with the vehicle shaking or vibrating at highway speeds. This is not the death wobble I have read about. You can feel the vibration in the seat like it is coming from the rear end, but not sure that is the source. I have bought new tires, had all four tires force balanced, changed out the wheels, etc., with no improvement. The suspension has not been modified. What makes this hard to poinpoint is that it is an intermittent problem, does not happen every time I drive it, and the degree of the vibration/wobble will vary. I have had independent mechanics look at it as well as the local Ford dealer. No one wants to take the time to try to diagnose the problem. They only want to balance the tires and send you on your way. I am not a mechanic and do not have a shop where I can experiment with fixes. If anyone has had a similar problem and found a fix I would be grateful to know what you figured out. Thanks in advance for any ideas.