Interesting misinformation. All three US truck manufacturers have DRW trucks with a 7,000 lb. payload capacity with their 3500 models.
With GM the rear axle load capacity is exactly 7,050 for trucks with the gas V-8 and with the diesel V-8. ONLY difference with the diesel engine is that the front end is rated at 4800 lbs. whereas with the gas engine the front suspension is rated for 4400 lbs. This is to be expected as 95% of the load in the box is supported by the rear wheels. The engine is supported by the front wheels oddly enough.
The camper mentioned is an ultra heavy camper and at this point one has to question the wisdom of buying such a camper and a heavy duty DRW truck to haul it around and pay double the cost of a Class C motorhome that will have more usable space.