The dealer is about the last place I would go for an oil change. Dmaxs take about 10 quarts of Rotella T plus the oil filter. GM engine computer tells you when to change the oil based on how hard the engine is being operated.
The fuel filter gets changed about every other oil change, plus the transmission filter. It has the Allison transmission and you just do not get much better than an Allison.
Maintenance may cost you more, but the engine is significantly stronger. Acceleration 0-60 under load is much better than gas as is the higher altitude performance.
I am not sure on 2011 engines, GM in its infinite wisdom, did not include a fuel pump on their 2500 series Dmax trucks. They have a hand prime plunger pump on top of the fuel filter (everyone else uses a $30 electric fuel pump). When the plunger rings get old the engine may stall when you start. The plunger assy runs $900, however, there is a $20 kit, and in an hour you can change those rings with a socket wrench, T-20 screwdriver using a YouTube video for guidance.
If you are going to pull a heavy load, I would look at diesels. When I was pulling 4,500# trailer with a V6 gas engine (Tacoma) at 6,000 ft up grades 50 MPH was max speed. Pulling 10,000# load up grades at 6,0000 ft with the diesel ate fuel, but I could maintain highway speed w/o issue.