You sound like me a couple of years ago spongebob, when I bought my first Duramax. I did a lot of research on what oil to use, & the only thing I found out for sure was that everyone had a different opinion. So I started doing regular oil analysis every 8,000 miles, just to see what gave me the best results. I tried Rotella, Rotella syn, Mobil 1300 Super, Delo 400, & Mobil 1 Truck & SUV. I think I did around a dozen UOAs total, & I even have a couple samples that I didn't bother to send in.
To be honest with you, there wasn't a whole lot of difference, but the one oil that consistently gave the best results was Delo. It gave the best wear rates, & was the only oil that held it's viscosity. The other oils would slightly thicken due to my EGR equipped Duramax. (I did one UOA with the EGR blocked to see what would happen. Higher TBN & lower SUS visc after 8k miles.)
I drive around 5-6k miles per month with payloads from 50 to 2000 pounds. I've had an '06 Duramax for almost a month now (4900 miles), & once I do a few short OCIs, I'll use Delo & change it when the Oil Life Monitor tells me to, probably ~10-11k miles. (I did a couple 10k UOAs & Blackstone always told me to go longer.) Next winter, I'll switch to a synthetic 5w-40. Not because it gives me better wear results (it never did in my '04), but because it makes a noticable difference during cold starts when the temperature gets below 10-20F.
The Duramax engine seems to be very easy on oil, especially compared to the 6.0 Powerstroke. IMO, I really don't think a synthetic oil is needed in a Duramax, unless you're really working it, or the temperatures are really cold. But do what you're comfortable with. After all, you're the one paying for it.
Sorry for being so long-winded!