The joints are not likely to suddenly fail. Put it in neutral with the parking brake on and go under to have a look.

See if you can find any play in the joint. Any is too much. Twist it, push side to side, etc. Look for any rust where the cross meets the cups. If it looks OK you can still go for a while. Just look occasionally as the miles begin to rack up.

Greaseables are better, but no need to change them till they begin to fail. I've changed a lot of greaseable ones that failed for no reason I could come up with. On older trucks with divorced transfer cases the joints between the tranny and the transfer case often ran at a constant angle and sometimes not enough to roll the needle bearings over a complete revolution. An old rule of thumb was 6 degrees driveline angle minimum to keep the needles from working in the same spot and making a dent in the race leading to failure. Also, I think, an automatic tranny is likely to help the joints last longer because of the reduced hammering from a solid drivetrain and occasionally a very large torque load.

A buddy of mine had one get so bad he was afraid it would come apart. Coming home from a trip he decided to stop and see what he could do. After digging around in the van he found a pipe cap that was close enough to maybe get him home, and put it in, in place of the old u-joint bearing cup. After babying it home, and making it, he drove to work the next day too. Then the next, and finally a couple of months went by before he finally changed the joint!

Then I snapped one once, on the axle shaft, by getting off the clutch too fast with oversize tires.

 

Mine stated squeaking (noticed at low speed, rear sliding window open). Good thing I replaced them when I did, the seal on one of the bearing cups was blown and the cup was full of rusty slivers of needle bearings.

When I jacked it up to diagnose the squeak, there was no looseness, just "squeak..squeak..squeak" when I turned the driveline by hand.

Honestly though, the remaining cups on both the fore and aft joints had plenty of grease in them and the needles were looking pretty healthy. It was probably just a fluke thing at 71k that ripped/gouged/blew the seal on the cup that went bad.

(BTW, Here's the rest of the story:
https://www.dieseltruckresource.com/...44#post2425044 )

 

that makes me feel better!! i will do the check that you told me. my truck is an auto which does help reduce shock to the shaft/differential. also, when i tow, when i take off; i roll into the throttle. when i hit about 2200-2300 rpms; i ease off the throttle which makes it upshift with no stress on it. i repeat this process untill up to speed. i think this will help trans/joints and diff. live longer. if it doesnt help; then oh well; it makes me fell better atleast.

 

I had the diff end joint replaced under warranty at 59,000 miles.

Then another one started to go at about 70,000 miles so I replaced the other two at that time with greasable joints.

Neither of the failed joints got "loose" just devoloped adriveline vibration.

The second joint that failed was the middle joint and it was seized basically solid in one direction.

When I removed it, cup was full of rust.

 

If you are chewing through ujoints at a acclerated rate, you really should have your drive shaft checked for run out.

My tail shaft had .150" runout when my stock joints failed at 39000 mile.

It took two driveline shops to finally figure out the problem, after the second set failed 10K later.