The techs at my stealership argued about this one. 2007 Sierra 2500HD 4x4 Manual says use AutoTrak II for automatic transfer case. Manual says use GM Manual Trans Fluid for manual transfer case. Operating instructions show 1. Automatic Transfer Case (push buttons) 2. Manual Transfer Case (Shift Lever) 3. Electronic Transfer Case ( different push buttons) Mine is electronic. One argument is that the Electronic TC is clasiffied as an automatic. The other is that it is manual, just with electric motors shifting instead of a shift lever. A number of dudes on other forums have different opinions also, however there are numerous mentions that Dexron III ATF can be used in the manual TC instead of GM MTF. A GM service bulletin confirms that. Okay - let's hear about it!