ALSO:
You must be pro-active.
No one can just afford to have his vehicle serviced by the dealer today anytime something breaks.
I have a good friend who has a one-man shop out of state and makes $300,000 a year working only with a helper (occasionally). His customers are people who were paying even MORE to dealers until they found him, and I think HE is outrageous (and I've owned and operated shops myself), but compared to the competition, his customers LOVE him, and he is a great technician (far superior to the dealerships at which he was trained at and worked for previously).
Join a Forum for Duramax owners (preferably ALL of them): http://www.duramaxforum.com/
http://www.dieselplace.com/forum/
http://www.dieselbombers.com/chevy-gmc-truck-duramax-turbo-diesel-forum/
and ask questions/research everything before you take your truck anywhere to get educated so you don't make yourself a victim.
Also go to:
http://www.duramaxdieselspecs.com/duramax-problems.html
as this is a "Common Problem" list for the Duramax engine.
I have a (stupid) cousin who spent over $125,000 at the dealership on maintenance on her Range Rover since she bought it new in 2002, culminating with selling it for $2500 for parts (in perfect condition in/out except for the engine, which was toast from aluminum chips after the timing chain ate through the nylon guide track into the aluminum backing plate). Free coffee, a Wi-Fi and a loaner-vehicle is NOT worth paying that much for.
I'd finally set her up a few months before her engine cratered with an independent Land Rover shop where she lived who charges HALF of dealer prices (but was still terribly expensive compared to DIY), unfortunately.
Things are expensive if you pay people to work on them, period, but starting with the most reliable vehicle to start with is your best defense (You can probably tell I am not a fan of the Duramax), and that you can do by reading and asking around to as many users as you can before buying, and then never buying new (where the first year depreciation is probably $10,000++ on a diesel truck as we're discussing).
Then you go in educated as you can be on your problem (via a Forum, like this one) to your tech so he can give you options. Avoiding being a victim is step ONE!
Lastly, there are sites online where you can ask professionals questions for a fee. These professionals will tell your their qualifications, and their position, so you can decide to pay them for their advice or not. Most in the automotive field are service managers or long-time technicians supplementing their income by selling their experience for a reasonable fee. Here is one on Chevrolet/GMC. You just ask your question, and see who comes up ready to help, then decide to "hire" them or not:
http://www.justanswer.com/chevy/
I hope you can find a good independent technician who will treat you fairly.
Sorry for the lecture, but either you have the biggest lemon ever built, or walk into the dealership with a target on your back you're not aware of.
Bob