Just so you understand. I tow a 12,400 pound fifth wheel with a Dodge Std Cab 4x4 Diesel rated to 8800 pounds. The truck weighs in at the mid to high 9000's with the trailer in tow(7K ready to tow with driver). As someone else pointed out most older 250/2500 4x4 diesel will be easily over the GVWR for the truck, but under the RAWR. The RAWR is what I watch carefully.
Another example would be an early 2000's Chevy 4x4 ext cab Duramax. Ready to tow with a driver it is around 7400 pounds, with a 9200 GVWR. So it has room for 1800 pounds of pin weight and extra passengers. Fords are similar.
Chris