You didn't mention the year of your Duramx. If 2010 or older you are pushing it . If 2011 and newer you would be OK. However as I have mentioned in other threads from my personal experience. I wouldn't consider a unit 15000 lbs or heavier that I couldn't order with IS suspension and disc brakes. Without those disc brakes you will have white nuckles when a light turns red in front of you. If you don't get the Mor/yde IS suspension your next question will be where can I get my axles bent as a form of alignment. I feel spending a little extra now will save a lot later. If wife can figure how to post a picture of a 15000lb Montana hooked to a 2011 HD2500 Duramax. Doesn't look overloaded to me and looks even better when Mor/yde got finished with the IS suspension. It now sits perfectly level. Back to the truck the 18 inch tires has the heaviest load rating. I am speaking for 17 ,18 ,OR 20 INCH STOCK RIMS.