The Duramax Diesel Supplement Manual is pretty clear on the subject and if you have an unmodified truck under warranty I'd stick with the recommendation (on the bright side almost all truck/automobile diesel stops have ULSD since it's
required by law on new vehicles so you won't have any trouble finding it), excerpt from the manual:
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Fuel - Use Ultra Low Sulfur Diesel Fuel (ULSD)
Use ULSD only. The emission control hardware used on the vehicle may be damaged by using fuel with high sulfur levels. Use only fuel that is dispensed from pumps bearing the ULSD label.
Do Not Use Low Sulfur Diesel Fuel (LSD)
Do not use fuel that is dispensed from pumps bearing the LSD label.
Do Not Use Non-Highway Fuel
Fuel labeled as off road or non-highway is typically very high in sulfur content and will damage the emission control system. Non-highway fuel is not intended for use in on-highway vehicles and does not have the fuel properties needed by the DPF-equipped Duramax diesel.
In addition:
. Use the correct engine oil.
. Do not add gasoline to diesel fuel.
. Do not modify the induction or exhaust systems.