Tom,
I had to replace the carrier bearing and rear U-Joint on my Tundra at about 130,000 miles. The symtom was a rapid vibration at 30 mph. It would go away, then come back again at 70 mph. I couldn't tell the U-joint was bad until I dropped the drive shaft. Once out, I put the UJ through its motion by hand. Doing this, I could feel how rough the motion was. When a UJ is new, it feels very smooth.
If you drop the shaft, mark its exact installed location. When the new UJ is in place, reinstall the shaft in the exact same position as it was originally installed. Drive shafts have a memory. If you don't put it back in the same position, you risk having some vibration.
I used a big hammer and a 1" solid steel bar to drive the old UJ out. It was a B&*(%$! to get out. After cleaning the shaft, I used my vise and a socket to seat the new UJ. This was actually pretty easy.
Some Fords have a small spring loaded thingy at the end of the drive shaft. I helped one of my co-workers swap out a UJ on his truck. This little thing basically popped out. It had disintegrated.. We weren't sure what it was. I got on line and found a blow up drawing of the shaft. The drawing showed the part. It has been a while, but this could be the thrust spindle they mentioned. If memory serves, it was a $15.00 part.
Tim