you can just ask nick about the 6.0 and the VG turbo it has and turbo lag not to mention the EGR cloging up. . .the vanes are natorious for sticking open causing the lag. now if they stick closed you'll overboost the turbo, float the head and blow the turbo.

the VG turbo on the 6.7's is a MUCH simpler design that doesnt use a rotating disk to open and close the vanes, it only has one moving part that pivots at the transition to the turbo.

also the duramax and the ford both use glow plugs to ignite the fuel as it is being injected into the cylinders. . .the cummins has enough compression to ignite the fuel like the larger OTR trucks.