After wading through hours of threads and every internet site in the world for an answer, and now being very confused,
what diff would a 4 speed early 2.0 sierra have, the code, what is left of it is G 4006 LC 38 2K2B.
To my reckoning that's a 3.38, any advances

This diff thing is driving me nuts

looks like a 3.38 to me
see this list
Push in type shafts

KC 3.14 7"
LC 3.38 7"
MC 3.62 7"
JD 3.92 7"
DA 3.91 7.5"

Bolt on shafts

BA 3.14 7"
GB 3.14 7.5"
DAA 3.14 7.5" LSD
FA 3.36 7.5"
AAA 3.36 7.5" LSD
AC 3.38 7"
CAA 3.38 7" LSD
BC 3.62 7"
BAA 3.62 7" LSD
AAA 3.64 7.5" COSWORTH (this has the same number as the 3.36 7.5" LSD BUT is ID'ed by 108mm drive flanges)
ADA 3.64 7.5" GRANADA COSWORTH
DC 3.92 7"
AA 3.92 7" LSD
GA 3.91 7.5"
ABA 3.91 7.5" LSD