Originally Posted by Keros

This post needs to get a lot more specific. Don't interpret this as me being a jerk, please, I realize not everyone knows all the terminology of everything.

There is no shaft into or out of the transmission that can be seen while the system is assembled. The front and rear propeller shafts mount onto the transfer case (t-case). The transmission's output shaft us buried inside the housing between the t-case and trans. The transmission is bolted to the engine, the t-case is bolted to the transmission. The t-case is in the rearmost position of the chain. rear shaft comes out the back of it, front shaft comes out the offset drop into the front diff.

If there's play in the front output shaft on the t-case, i.e. that it moves L/R, then yes, the bearing that holds that in place is toast. All other diagnostics can stop here. That mount should be completely stationary with only a tad bit of axial (in and out) and wobble (L/R & up/down) play. If it moves a lot then that's what's banging around. I think Randy's fielded this in prior posts.

The front half shafts (between the front diff and the wheels) tend to scream bloody murder if for some bizarre reason they have enough wear in the cages to allow freeplay/slop. There's oodles of contact surfaces in their design that having them wear out to the point of notable rotational slack (where one end is stationary and the other can be freely rotated), prior to them breaking or the bellows being blown out and vomiting grease everywhere... is virtually impossible. I'd ashamed to admit I drove my 3rd gen 40,000km with a half shaft bellows torn wide open and no real amount of grease likely in it. And it didn't make a peep of a noise or have any play in it. It seems entirely unlikely this is the issue.

Rotating the input shaft of the front diff should make the wheels spin. There's no ADD systems on the V8 (full time), so both wheels should spin the same direction when you rotate the input. You should feel there is a tad bit of play available in the diff's input, but just a little little bit. If it feels like the pinion clunks into the ring gear when it changes direction then yeah, that ain't right. The kind of play it should have is like the thickness of a piece of paper, in and out and rotationally.

If it were my rig, after looking at these things and it all seems okay, replace the front drive shaft. The shaft needs to change length slightly as everything moves together. If the extension tube has worn itself a ridge in the sleeve, it'll catch on the ridge, build pressure, then release, as it's compressed (hence, a light clunk under braking). I recall reading that the Toyota shafts have very tight tolerances, so I'd imagine it wouldn't take much to have this happen.

All speculation, though.

If you can get under the truck and take a video of it, that would help us make better wild speculations.