I ran my 11' camper on an '07 Chevy 3500 SRW for a while. It weighed at 11,140, the truck's GVWR was 9,900. Then I upgraded to an '05 Chevy 3500 DRW. That rig weighed 13,100, it's GVWR was 11,400. I was not over axle or tire ratings on either truck. I traveled many thousands of miles thru multiple states for years with both trucks. I never had any problems.
The rear axle on a those trucks was the AAM 11.5", it is rated by AAM for 10,200 pounds. I was no where close to that kind of weight, the axle was safe. I also had air bags added to both trucks so they were taking significant load off the springs so the springs were safe too.
I was well under the truck's GCWR so the drive train wasn't being stressed beyond it's design limits. Really, the only thing possibly questionable would have been the brakes. But in 36,000 miles I never had to do any brake work on the SRW until I sold it. The dually brake pads did need to be replaced at 185,000 miles.
Nobody that really uses a truck like a truck pays attention to the GVWR except RVers. Farmers, contractors, and commercial haulers, and the DOT all all go by axle and tire weights if they even weigh or check at all. I used to work for a compnay that had an '03 F350 with a GVWR of 10,000 I think it was. When that truck was loaded up to 12,500 pounds one day (according to the landfill scale)I noticed the overload springs weren't even engaging. So, yeah, I think Ford designed it for a bit more weight.