What Rear End

[jsjmall4]

vin # 2GCEC19T631334154

[gmtech4]

you have a GU6 rear diff 3.42 ratio,parts dept can do the same thing,pick up the phone,its faster,lol.

[pwall]

vin # 2GCEC19T631334154

If you have access to the vechicle (assuming it's not yours), all the RPO codes are listed in the glove box.

On this site, top-left corner is a link for 'RPO Lookup'.

Here are some of the RPO codes for the rear-gears (of course there are plenty more):

For a 3.42, the code is: GU6

For a 3.73, the code is: GT4