Transfer case fluids ?
 

I have 2 trucks,K1500's, a 97 GMC 6.5 automatic 4x4 with a floor shift transfer case, and a 98 Chev 6.5 automatic ,4x4 with a push button transfer case .
I keep getting conflicting information on what fluids to use in the transfer cases. Both are high mileage ,and probably have never been changed. I don't want to go to synthetic , but some sources say the 98 push button has to have synthetic, and the 97 takes DEX III, .
Also how many liters/quarts does each take ?
Thanks
Pete