Curious how you determined this, you had the fuel tested??
Has anyone tried something like DPF remedy to decrease the sooting of the exhaust?
Kindly see the Duramax Diesel Owner's Manual Supplement where they explicitly recommend against additives of any kind in the fuel.
The manual states that any warranty claim issues caused by additives may not be covered by warranty ... and if I know GM ... they will look for any way to get out of warranty due to additive use.
Honestly ... I drive areas that can get down to -40 deg in the winter ... so I do carry Power Service 911 with me to dissolve gelled fuel at these low temperatures (emergency situation only).
Only once have I had to get under a truck, remove the fuel filter because of gelled fuel plugging the filter, and that was a company Ford F-450 in 2008 (Big Piney, WY at -35 deg F).
They blend in #1 diesel into #2 diesel where I live in the winter to lower the gelling point of diesel, so it has to be very cold to have issues.
But in case of poor blending, I also add Power Service Fuel Supplement when I will be traveling where temperatures are below 10 deg F.
Since I am a chemical engineer (BFD some will say), I know this product is not an emulsifier or other additive makeup that could cause damage, and Power Service (parent company) sells this stuff by the barrel to the trucking industry with years of proving no harm will be done.
But in the end if GM wanted to push the issue because of a warranty claim ... and they were denying the claim saying they could prove it was the additive ... I am willing to take that risk in an emergency situation only.
Of course ... all of this is just my personal opinion(s) being stated ... just afraid to be the Ginnie pig since these L5P's have so many sensitive sensors that are very expensive ...