Hey, as long as the correct rating (or better)required for your Duramax, do it! I come from Rotella T, 5W-40 for the last 12 years. Started running just Delo, heck, I'd run Napa, I'll check.......and wouldn't you know??? Delo, we bought a pallet of it for just a hair over $10.00/gallon at Costco.....same mpg, same performance, motor doesn't act any different. Synthetic, I'm sure it has it's place, but there's a lot of "snake oil" out there. Run it! : )