I hope Chevy relocated their DEF tank. Last year we looked at a 3/4 ton 4 door long bed. They had the tank hanging 4" below the frame right behind the right front tire. There's no way it could survive even limited off road driving. A service man just happened to be standing there & he said they were staying busy installing aftermarket shields to protect them.
You either need your eyes checked or a new tape measure. The DEF tank is essentially flush with the frame.
99% of the population wouldn't take their CC long bed truck the places I take mine during deer and elk season. Its funny how the DEF tank has survived just fine.
