No, that's not a 4500, its a 3500 with ordinary 17" wheels and tires. A 4500 would not sag a bit under that load. I have a 3500 with a flatbed and boxes plus a 75 gallon fuel tank and fifthwheel hitch. It will sag about 2 to 3" under the heavy kingpin load of my 14k fifthwheel or 10,000 lbs. of gravel in a gooseneck fifthwheel dump trailer. That's about as far as the rear springs will depress and about 1/2 of what a dually pickup will sag.