Duramax Fourth Generation: 2007.5-2010 (LMM)
Truck: 2009 2500HD
Mods: none (yet)
I'm looking for assistance in diagnosing my slow decline in mileage. I've been tracking it for awhile as shown on the graph, and I'm trying to determine whether this might be an injector issue or something else. I've been fairly diligent on...