I've got a 2000 5.4 4x4 with 241k miles.

Occasionally when I get on the gas (after coasting or starting from a stop) I'll get a knock that is felt somewhere under the truck. Not everytime. I've checked the u-joints on the rear driveshaft and couldn't detect any play. I lubed the slip yoke with some Motorcraft grease with PTFE which cured the knock I would hear when backing off the curb in front of my house. The front right CV needs to be replaced- boot has been torn for awhile and grease has been slung out everywhere. Haven't checked front driveshaft (brown wire mod so no power should be going through the front driveshaft). Rear axle seals are weaping a bit and I have added some fluid to the rear diff- could be low again.

What about motor mounts? Transmission mount? Rear Pinion? Other ideas?

Thanks alloro. I'll look into that.