There is the rear axle fluid (that uses ACDelco 10-4034 Dexron LS 75W-90 Gear Oil [88862624]) and
the eLSD (that uses ACDelco 10-9394 Dexron VI Automatic Transmission Fluid [88865601].
Mobil I sell both in synthetic versions,
I have used the transaxle version for years in the diff of my 99 C5 and also the Dexron ATF version in the manual tranny