had a sliverado 1500 and now have an F350. Both look like pickup trucks.
BUT that's about where it stops.
The 350 has heaver frame (thicker steel), extra support on the driveshaft (like medium duty trucks), huge brakes, free float rear axle, 8 lug nut wheel/hubs, 10 ply tires, MUCH bigger brakes. Much bigger springs as well.
Difference between, say a bicycle frame and a motorcycle frame.
The entire dynamics of the vehicle are different - a 1500 is a CAR. A 350 is a work truck. The 250 is a nice middle ground good for light work or heavy 'consumer' use.
Folks overload all the time. I've run at the limit of one thing or another at times - and survived.
Like my Kioti - rated to lift 1800lb on the loader. Even if that isn't including the bucket/forks, I should get 1500 real lift, right? Nope. 1000 give or take 50lb with loaded rear tires. And it's sketchy as all ****. PUt a big implement on the back (1000lb-ish) and it keeps the rear wheel on the ground more consistently, but it's not a load you're gonna wanna go fast with , lift high, or go down a grade with.
So there is a rating...how/where they get it I'm not sure. How much margin of error is there? Is your truck NEW or worn? How much does that rating drop with non-oem brakes/rotors/shocks, wear and mileage?