Although today's 3500HD is built with a pickup cab, they have more capacity than the old 3500 with 20". The wheels are 17" duals with 8 hole metric.

https://plus.google.com/11263693037...5156051106&oid=112636930370126476644

Thee trailer has 17.5 singles that carry as much as 16" dual with a lot less rolling resistance. Although I have a CDL, the single tires keep me under the radar with DOT hassle. Most troopers haven't been taught that 17.5 singles carry more than16" duals.
The term HD with a GMC is not just a macho term. Take a look at a 2015 3500HD GMC. It amazes me how they are build, and I have been around trucks for over 50 years.