I have a 2002 f-150 Fx4 with 102k and I think I figured out the problem from reading different forums, but thought I would see what you all thought. When I am running down the highway in overdrive and I press the gas hard enough to accelerate, but not kick out of overdrive I feel a vibration in the truck, but as soon as I let off it is perfectly smooth. What I read says it is probably U-Joints.

Any ideas?
Thanks

 

Hop underneath and grab your driveshaft with both hands and see if it wiggles, i bet your universal needs to be changed, you notice it more at higher speeds, less are low speed and rpm

 

Ya I did that and there was not to much wiggle, but probably enough to cause a prob. Definately worse at higher speeds.