I too am a little skeptical of the numbers you were given.
Even the 2014 chevys with the 6.0 arent listed to tow that much. But the internet is full of inaccurate information, so what I see may not be accurate.
The site I linked earlier dont even list my dodge's configuration. (3500 DRW Quad LWB with 3.73). Only lists 4.10's.
Dad owns a 2004 Chevy DRW 6.0 and 4.10's. Its got a whopping 9700# tow rating.
For 2014, I didnt see any gas engines capable of towing over 16k. Had to go diesel to get over that mark. I just dont think a truck of 10 years older with gasser is there. Especially bumper pull with a heavy dump body.
You guys got to compare apples with apples. Cab and chassis trucks usually are rated a little different.