What type of differential fluid to use for AWD optioned Tahoe?

[Brewcity]

Hey guys...I have a 99 4x4 with the AWD (push button) option...what type of front and rear diff fluid do I use? Not sure on what type of rear differential I even have. I have read 75W90 synthetic for both front and rear...is this correct, and if so...does the rear need an additive? Can I (should I) use something like Mobil1?
Also...where is the filler plug. I cant seem to see it.
Thanks for the help with this. I really appreciate it!

 

[SunlitComet]

that is about right but the rear does not require synthetic so it is optional. the front is required to have it. Do not use any additives at all front or rear.

 

[Brewcity]

that is about right but the rear does not require synthetic so it is optional. the front is required to have it. Do not use any additives at all front or rear.

Thanks a lot for the clarification, and the help.
I really appreciate it.

 

[Brewcity]

BTW...with no drain plug on the cover...how do I know how much to put in?
On my Jeep...it was until it starts to drain out the drain plug. That cant happen here, so how much oil do I use? And can I use the blue RTV for the cover with the gasket?
Thanks for the help!

---------- Post added at 03:56 PM ---------- Previous post was at 02:17 PM ----------

Found the filler hole (I think)...behind the cover on passengers side. Is this correct?
If so...I just fill until it comes out that hole?
Thanks for the help!

 

[ezdaar]

its on passenger side of the snout, use a socket wrench and 4" extension. Just look for the plug and shove the extension in it.

Most are a real PAIN IN THE @#$ to get out so be prepped.

 

[Brewcity]

its on passenger side of the snout, use a socket wrench and 4" extension. Just look for the plug and shove the extension in it.

Most are a real PAIN IN THE @#$ to get out so be prepped.

Great...thanks for the pic. Mine is a little above where yours is...and it was a TOTAL pain in the arse to get to budge!
Can I use Blue RTV on the gasket and cover?