I'm using Delo 15w40 only as we speak for my rebuilt 6.0 lq4 going back in the 04 below.
_________________________
04 2500hd 6.0 258k/18k edg 0w40 XG3675 VML ATF PGL
03 C7500 Dmax7.8l 134k ST 15w40,M1ATF Dexcool
06 2500hd 6.0 197k ? 5w30 ST DexVI PGL