OK, I am even confused now!!
Lets see if I can help confuse things further.
Front Diff-- OEM fluid is 80-90 gearlube. It is acceptable to replace it with 75-90 synthetic fluid. Any quality fluid is acceptable as long as it meets GL-5 requirements. When going to any type of synthetic fluid, its advisable to change the vent cap on the front diff to the "white" cap. This cap is the replacement cap and the black cap is no longer offered. Part No. 12479296 for the cap. The refill capacity for the front diff is 2 quarts.
Transfer Case- First, lets discuss the options for the transfer case. If you are driving a 2500 HD or 3500 pickup, you have a NV-263 case(push button shift) or a NV-261 case ( floor manual shift) There is no automatic transfer case in these trucks. The 1/2 trucks and I believe the 2500 (non-HD) trucks will use the NV-241 (floor manual shift), the NV-243 ( push button shift) or the NV-246 case ( auto-trak, push button ) We will concentrate on the 2500HD and 3500 trucks here. The OEM fluid for these is Dex III or equiv. This means that any quality Dex III fluid or synthetic will work. There is no changes necessary to switch to synthetic. Capacity is 2 quarts.
Rear diff- The 2500HD and 3500 trucks use an American Axle 11.5" rear end. Its available with the Eaton limited slip option (G80). The Diesel engine equiped trucks only come with a 3.73 gear. The 8.1 trucks have either a 3.73 or a 4.10 option. The OEM fluid is 75-90 synthetic
lube, commonly referred to as "grape juice" for its smell. A synthtetic lube must be used in the rear axle and it must meet GL-5 requirements. I dont know the additive package of the aftermarket lubes but I would think that the quality lubes contain the necessary additives for the limited slip. It is not necessary to add any additive to the rear end when servicing. Capacity is 4 quarts. It is recommended by Eaton to service the rear axle after the first 500 miles of towing or 5000 miles of driving.
I hope this helps out a little