Using the incorrect type of transmission fluid in a manual transmissions or transfer case may affect the sealing ability of the seals. An incorrect type of sealer may not be compatible with the transmission fluid or may not have the correct characteristics for sealing the affected components. An incorrect type of fluid may also have adverse chemical reactions with materials used in the TC or trans leading to premature failure of components.
If it says AT use AT, if it says Dexron use Dexron.'
DO NOT use Dexron VI in place of manual transmission fluid in any manual transmissions or transfer cases that specify Dexron III, as a failure may result.
Amsoil was working on reverse engineering a fluid for this application but nothing yet. From the NNBS 2007 on the requirement is no longer AT-II, its Dexron VI.
BTW-I stock AutoTrac II fluid here for customers and it costs me less than $10 a qt. I get thru a AC Delco dealer, not the GM dealer. Dealers are 2x and 3x the price from AC Delco for the very same parts. TC should only use about 2 qts, if that.