Changing the fluid in the Differential

I am trying to slowly take care of maintenance things that are in need of being done. One of them is changing the rear differential fluid. Since I am not rich and try to save money when possible, I was looking at doing this myself. I tried searching the forum, but did not come up with a definite answer.

So, I have a 2000 5.3l with 3.42 gears. The only code related to the rear end that I can find is GU6, which is the gearing. I do not see anything that leads me to believe that the differential is anything special, since the truck did not come equipped with the towing package. There is a blue plastic tag on the differential that says to use synthetic oil. I have read that the oil from the dealership is around $27 per qt. I have seen Mobile Synthetic in the same weight at Autozone. My question: Is this a safe replacement or is there a special additive in the GM oil that is not in the Mobil oil? Also, is there anything special that the dealer (or independent shop like Firestone) is doing to justify the $140 charge for "differential service"? I don't have a problem with paying for the GM oil, or the service if there is a true necessity for it.

Any advice is greatly appreciated.

Sincerely,
Matt

I run Mobil 1 75W-90 in my Yukon and have had no issue. No special additive is needed. If an additive was needed, it would be on the blue label.

//2000CAYukon

Thank you sir!! I will do just that then, along with a gasket change!!

Sincerely,
matt

$140 is way too much. $10-15 per qt for synthetic, you'd buy 2 bottles, plus a new cover gasket for $8.

The 3.42s are typically open differentials, but G80 or G81 on your RPO list would indicate a limited-slip or locking differential (aka positraction), respectively. No special additives needed unless the G80 is listed, and even that is sometimes debatable depending on the oil you use. Some diff oils have the slip agent included, some don't.

Yeah, there is nothing on the build sheet that indicates a G80 or G81 anywhere. There is nothing that indicates it on the tag on the diff, so I am thinking I am safe.