2010 FX2 5.4-recently when I accelerate from a stop I feel a "thud" immediately after depressing accelerator. Feels like something breaking loose or "giving" in the drive train. After initial movement within a second it happens. It is not drastic but I feel it. The truck will be at the dealer next week for service and I kind of want to have an idea what I'm facing when I tell them about it. The truck has 54000 miles. If I accelerate while in motion, as if slowing to stop the re-accelerating it doesn't happen. Just from a stop. And if I accelerate very slow and gradually it doesn;t happen. Another post I found regarding a similar issue suggested that the slip yoke needed to be lubed. Any input would be appreciated. Thanks