This is what we got from Yukon Gear & Axle: an installation kit, which consists of bearings, seals, and a 3.21 ring-and-pinion set. | 
To get started on the swap, the truck was secured on a lift, and the axles were removed. On heavy-duty trucks like this one, the axles are full-floating, held in by the bolts on the hub, as opposed to C-clips in the center section. | 
With the axles out, the technician moved under the truck and removed the inspection cover. Once the old smelly fluid drained from the housing, the bearing caps were unbolted. |
This allowed the carrier to be removed from the housing. It was set aside for the time, because there was still some stuff in the rearend that needed to be removed. | 
On these GM 10.50 Corporate rearends, aka a 14-bolt, the pinion assembly actually unbolts from the front. So, unlike some of the more common 1/2-ton trucks we work on, this one was a little easier because we could set up the pinion on a bench, instead of under the truck. | 
After the bolts were out, a few taps from a hammer and drift drove the pinion assembly out of the housing. |
See! Now if this was a, let's say, 12-bolt rearend, we couldn't do that. | 
With the pinion assembly out, the technician went ahead and popped out the straddle bearing that was still in the housing. | 
Another cool thing about the 14-bolt is the diff housing; it has built-in threaded carrier pre-load adjusters. These make gear set-up much easier, and we like easy. |
Here, the technician is using a puller tool to remove the carrier bearings from the carrier. | 
Now to actually start changing the gears, the pinion support assembly was slid into a press after the nut was removed from the yoke. He used the press to push the pinion out of the yoke, which, in turn, allowed him to remove the pinion bearing retainer-the big cast piece below the yoke. | 
Here is a snapshot of the new ring gear (left) that will be installed on the factory carrier. |
With the aid of an impact, the bolts were removed from the carrier. Don't expect the ring gear to just plop down on the bench because it will take the persuasion of a hammer to get it loose. | 
All of the parts to be reused in the rearend were thrown into a wash for a good cleaning. | 
The new Yukon gears are very nice, but a little de-burring with a grinder will ensure no little casting fragments will come loose and also make the gearset a bit quieter. |
Once the tech was done with de-burring the gearset, he installed the new parts onto the old stuff. The new ring gear was pressed down onto the carrier and held on with new bolts. The pinion was also installed with the new bearings from the installation kit, along with a new crush sleeve. | 
Here is what the pinion assembly looks like with all of the new parts, compared to the leftover stuff on the left. | |