I just changed out my rear 2 U-joints a couple weeks ago. It came out pretty easy once I had the right tools. Start first by putting the truck in park, press the parking brake, and chock all the wheels. Have a helping hand. Have the other person hold the 14mm bolt with a 14mm wrench. You (or the stronger person) use another 14mm wrench to remove the 14mm nuts. (I am referring to the 14mm bolts attaching the driveshaft to the rear diff). Use a hammer and bang the the end of the driveshaft until it separates from the rear diff. Remove the carrier bearing via the 2 bolts. I forgot the bolt size but I want to say 14mm as well). BE CAREFUL and have your helper hold the driveshaft so that it does not injure one of you or gets damaged. Slide the driveshaft out of the slip yoke.
Remove the "C" clips on the rear U-joint. Use a big socket or something similar (cylinder like), and place it below the yoke (the other end of the U-joint). This lets the U-joint come out of the other side. Use a socket that fits inside the yoke and attach a socket extension. Use a hammer and pound it out. Don't go too far or else you'll damage the yoke with the U-joint. Continue this for the rest of the U-joint(s). I changed out my rear one because it was shot. I also changed out my middle one because I don't want to wait for it to brake. The one closest to the cab is known to last a while.
I hope my instructions were clear enough to help ya out. I had no one tell me how to do it and I just winged it. It took me about 4 hours with Will (DaWillDaBeast). Make sure you have a grease gun if your new U-joints have grease zerks.