Need help fast!
Rust is a big thing here. When you're working on the truck it seems like every nut and bolt you come to is rusted to some degree. Some are so bad that the bolt will break before the nut comes free.
After you drop the shaft give the threads on the U bolts from each end a good cleaning with a fine wire wheel or wire brush.
When you get to the bearing cups that were pressed in give the area around the retaining clips a good cleaning and soaking in WD-40 or rust buster before you attempt to remove them.
After the old U joint is removed give all of the areas where the bearing cups sit in the yoke a thorough cleaning. If you cut the handle off a 1" tubing brush and mount that into a 3/8" drill it will make the job a lot easier.
Finally, make sure that the channel that the retaining clip sits in is pristine. It's a tight fit between the channel & the clip and any dirt or rust in there will give you problems later on.
I use never seize on a lot of things. If you give the place on the yoke where the new bearing cup presses in a light coating it won't take nearly as much force to install it.
Be careful with the cups though. When you take them off the U joint it's possible to lose one or two of the needle bearings inside. If even one falls out and you don't notice the job won't be right and it will give problems aterward.
Sometimes the job goes easy and sometimes it goes hard but taking the time to clean & lubricate gives you a better chance of having things right you're finished.

