Greasing Sealed U-Joints?

Unless you remove the drive shaft it's just a picture of drive shaft. Once it's out you can move the u joint and actually feel what it's doing if all is good you should feel no resistance if it's dry or just shot you will know. The diff end moves more than the front so you really need the entire drive shaft laying on the floor.

 

OP your truck is nearing 100k. Replace the U joints and carrier bearing (if equipped) as scheduled maintenance items. Then go from there.

 

My 15 has zerks for every U joint from the factory.

 

My '11 also has zerks on every joint, however Toyota discontinued the serviceable U-joints years ago and I went with the current part number when replacing mine.

When I serviced my driveline I first bought the Spicer greaseable U-joints but returned them because the dimension across the caps was too big, no way to get even the thinnest retainer clip in the yoke.
There should be no issue with the non greaseable joints unless they are improperly installed. The seals are designed to keep contaminants out, versus the greaseable type which are designed to let the old grease and contaminants purge out. The greaseable seals will let water in.