It is its own recommendation.
GM PN 97779615
Isuzu PN 2-90531-200-0
This is a heavy duty transmission. As such, we don't know if it is something simple as T-IV or something archaic like DexronII.
But, most here know that I wouldn't use the 'factory fill'.
Those who say it cannot be done, should not interrupt the person doing it.
Your automaker lied!
Is this a spelling/grammar forum or BITOG?