'02 Pickup axle noise
 

I normally just do olde trucks, but my friend is going to show up at my house so I can help him figure out why his rear axle is making noise. So I have some stupid questions:

1). What axle does a 2002 have? Is it still the 10-bolt, 12-bolt thing, or is it something else? How about interchangeability when we go to the junkyard?

2). He says is it has a locking differential option (uh-oh). Is this still the grenade 80?

3). The truck has a 3.73 in it. Will it screw up the computers if we change ratios? He drives it mostly on the highway and doesn't really tow.

I told you they were stupid questions. Anything else you can think of would be appreciated.