I've never done u-joints so I can't help you there. I will say this though, use a paint pen or something to mark the orientation of the driveshaft before you remove it. IE where each end bolts up to the differential and the t-case on the drive flanges, and where the splined end of the shaft enters the main part of the shaft. You will want to re-install it in the same orientation as it came out.

Also as said earlier, while it's out give the drive flanges on the t-case and differential a good wiggle to check for movement. I've had vibrations come from those areas before that were fixed by re-staking the nut.

 

ive done u joints many times, you will want access to a vise at least. and as far as marking things thats the right idea but the wrong locations. mark each end of the driveshaft on the flange and where it mounts to the rear end and t case. then mark each side of the splined part of your driveshaft. as far as the ends of the d shaft they only go together one way, the u joint looks like a cross and only has 4 sides , you cant reassemble that part wrong, it simply wont go toghether right

 

This was the cause of my rumbling. I swapped out the U-joint closest to my transmission. I still have one CV joint to replaced just because the boot is severely damaged (not sure how long) but since I replaced the passenger side I might as well do the driver side.