FWIW I have a 2015 Silverado 2500HD except I have the 6.0L Gas.
My yellow sticker gives me a maximum payload of 2853lbs. My trailer has a tongue weight of 975lbs so minus that from 2853=1878. So I have 1878lbs left for passengers and "stuff". The max GVW of my truck is 9500lbs, the max GCWR (truck and trailer combined) is 20,500lbs. Max trailer weight listed at 13,500lbs, my max trailer weight is 9500lbs. I'm not a FW expert by any means but it would seem that a pin weight of anything over 2500lbs would be close if you put passengers and stuff on top of that.
Your Duramax figures may be slightly lower due to the weight of the diesel.