Looking for help with vibration at 45 to 55
 

First of all I'm New here and want to thank everyone in for participating in such a great form. I've been looking for a thread but can't find exactly the answer. I picked up a 2015 f150 platinum fx4 with the 3.5 ecoboost. I love the truck other than a vibration that starts at 45 or so and gets pretty annoying at 54mph it seems to go away about that. Vibration completely goes away if you let off the gas but the minute you put it back on it resonates through the whole truck . I can feel it in the steering wheel, gas pedal, and whole truck. It hits a harmonic note that sounds like deep bass and rumbles through the vehicle. I've taken it to the dealer and they are saying it's a characteristic of the vehicle. They did drive around with me with a laptop hooked up and looked for a misfire or something like that and found nothing the computer could figure out , but I think it's more in the drivetrain . I told them that it feels like you are in a stick shift car and need to downshift and they said that it might be turbo lag. So I've been driving it around and trying to downshift manually and it doesn't go away. It has the one piece driveshaft. Vehicle has 42000 miles on it. Again if you can point me to the right thread or any ideas would be greatly appreciated

I'd check the u-joints.

I bought a new 2017 Super Duty and the day I drove it from the dealership I noticed a vibration that didn't seem normal. I turned around and went directly back to the dealership and they found all four tires out of balance. The right front tire and wheel was 2.75 ounces out of balance.

thank you for your suggestions. So after taking a few test drives with the service manager. He tried disconnecting one of the exhaust mounts and thought it was a bit better. Then he reinstalled it and actually took a drive shaft out of a brand new 2017 and installed it in my truck then we went for another test drive and lo and behold it seems to have gotten rid of the harmonic residence through the truck. Couldn't be happier right now. I really want to love this truck. And now I do

Excellent!