Truck GVWR of 9k here. Weighs 7900 with fuel, me, toolbox, and tonneau. With the trailer ready to camp my truck weight is at 8900lbs (4300lb measured on rear axle, way below axle & tire rating), but that is before the family, generator, and anything else I may shove in the bed. So I'm over my truck's GVWR 95% of the time I head out with the camp trailer.
My truck has scaled over 10k a few times. Two 650cc dirt bikes (over 300lbs each), four guys over 200lb each, generator, extra fuel and water, another cooler...
I do not have any aftermarket suspension assist (just stock springs without factory upper overloads), just the Equalizer 4-way that is set for my 'normal' load for family trips. I do not adjust for the trips to Moab with the guys (when I know I'm running heavier on both the truck and trailer).
While there can be other differences between 250/2500 and 350/3500 besides springs (like when Ford ran 17" wheels on the 250 but 18" on the 350 in the mid-2000's), many times it is as simple as a different spring pack for the rear such as on my 'older' Dodge. I carry what I want without regard to the truck GVWR. I did get the rear axle to 5600lbs once with a bed full of gravel (2500lbs worth), and if I was to carry that amount of weight on a regular basis, I would get bags/timbrens/ect to help carry the weight.
