Driveline Clunking

[win9x23]

My truck started to make random clunking noises, now when I start moving I get a rather loud "clunk". Stepped on it the other day and it started vibrating badly, so I eased off and made it home. Thought it was the u-joints but they all seem pretty tight. In Park there is no play in the rear shaft, but the front shaft rotates about 3/8" inch (measured on the outside of the u-joint) so I think something is bad in the front diff or transfer case.

Is there any easy way to tell what is bad here w/o a complete disassembly? Tx!
(1999 XLT 5.4 w/ posi rear).

 

[Jrod1990]

My 4.6 XLT did this the other day, it sheered the bolts off that connect the trans tailshaft to the T/C, dumped a bunch of fluid too when it mangled the gasket there. Also found out the rear u-joint on the front shaft had a bunch of play in it too. Have you checked the fluid to see if there's any metal in it?