Maybe I'm adding confusion to this subject.
Apparently, I was informed wrong when the dealer upgrade bulletin was issued, that the additional fluid would not be required on vehicles after the VIN I posted. It appears the additional fluid is required, but rather than issue a bulletin, there is a note added to the t/case informing the tech to add the additional fluid.
So, it appears that all t/cases, at least in 2006, require the extra fluid. I will check on this tomorrow with engineering.
HAL: As for the manual, the electronic manual I access online is updated daily with new or revised information. For the engineer to update the information is very easy, put in a request, and a day or two later it is available to the dealers via the GM electronic service information website.
If I find out tomorrow that all cases required the extra fluid, I will notify the people in charge of service manuals and have them make the change to the fill procedure.