^^^ Any parts store has these. Kind of a pain but not a hard job;
What I do;
If I remember I spray some PB in there a couple of days before.
Mark the DS and the Diff Flange so that you can put the DS back in the same way.
Then disconnect the DS from the rear diff (4-17mm bolts/nuts).
Drop and slide the DS towards the back of the truck; the whole thing slides right out. Take out the c-clips (4) holding the u-joint in place.
Knock the old u-joint out with a socket (my 17mm impact worked for me) and a BFH stopping when the Journal bottoms out. If you go too far you bust the caps making it more of a pain to remove.
Once it's bottomed out, if the one side hasn't fallen out, grab it with a vise-grip and then hit the vise-grip with a hammer...should pop right out. Hammer out the other side with a smaller socket. Vise-grip/hammer...
Clean out the ears of the DS and Fkange removing any rust and/or debris, especially the groove that catches the snap-rings.
I put some tacky grease (RCV) in the caps so the needle bearings don't shift when I hammer them in and anti seize in the ears...especially the groove that catches the snap-rings.
Press the new one by tapping the caps with a hammer, finish with a the socket.
Put in the 4 new c-lips that comes with the new u-joint.
Slide the slip yoke back in careful not to damage the TC seal and connect to the diff.
Torque the bolts to 58-65 ft-lb.
Done.
If you have a press you can use it making sure you don't over press. I made the mistake of using one too much and busted the cap making it more of a pain to remove.
I know most folks prefer the socket/BFH method even when they have a press. Some start with a press to break the u-joint out of the rust and finish with a socket.
You can get greasable or sealed (non greasable) u-joints. I prefer sealed; I think they last longer. It is debatable and ether one will do the job and would be correct.