I'll post this here, but not sure if its the correct place.

Simple question: What is the rad-like object on the front of the fuel tank?

It's the return fuel cooler. Fuel is pulled through the two Fuel Injection Control Modules (FICM) mounted on the valve covers to cool the electronics, then the fuel filter by the low pressure (gear type) stage of the fuel pump. Then it is compressed in the three plungers of the high pressure stage of the fuel pump up to 20,000 psig for the common rails where it gains tremendous heat of compression. Some of it is bypassed by the fuel rail control valve, some of it is bypassed by the injectors themselves. This hot fuel returns to the tank through the return fuel cooler.

It is a fuel cooler. The high pressures the injection system runs under produces a lot more heat than former systems.

It's the return fuel cooler. Fuel is pulled through the two Fuel Injection Control Modules (FICM) mounted on the valve covers to cool the electronics, then the fuel filter by the low pressure (gear type) stage of the fuel pump. Then it is compressed in the three plungers of the high pressure stage of the fuel pump up to 20,000 psig for the common rails where it gains tremendous heat of compression. Some of it is bypassed by the fuel rail control valve, some of it is bypassed by the injectors themselves. This hot fuel returns to the tank through the return fuel cooler.

Thanks for the response and explanation. I'll make sure to clean it out when I'm washing the truck.

The little rad like thing is in fact a return fuel cooler.

But I can not agree with the other explanations of it's purpose.

In my opinion/experience, I think it's sole purpose is some idiots idea of a way to keep from melting or disintergrating the plastic fuel tank.

When guys like you and me operate a vehicle equipped with a fuel cooler,
located under the truck, here in Alberta, we very shortly find out that it is totally clogged with "Gumbo".
Question to ponder: What cools the fuel when the fuel cooler is clogged?

Possible answer to numerous Duramax fuel injector failures:
Plastic resin from overheated "Decomposing" plastic fuel tanks clogging injectors.

I have personally found decomposing plastic fuel gage floats located in steel fuel tanks, on recent Caterpillar built equipment using no fuel cooler and using high pressure diesel injection systems, to be the cause of numerous fuel supply problems.

If it was important to cool the fuel prior to it returning to the injection pump or FICM, why not use a engine coolant heat exchanger, similiar as to what is used for cooling engine oil or Hyduralic oil systems to engine operting tempertures????????

Just my thoughts on the subject

Have fun trying to wash the dried "Gumbo" out of your fuel cooler, mounted underneath your truck.
If you find a wash bay with a step-down grease pit, let use know.

^^^ hahaha you know... your thoughts are mine exactly.
The reason I asked the question is b/c it looked to me like it was a fuel cooler, but like you I couldn't understand why they put it under there.

So I spent 2 hours yesterday cleaning out the mud and rocks from my frame and in the process I cleaned that fuel cooler.

Offtopic, but did you know that when you remove two wheelbarrows full of mud from the underside of your truck it likes to ride better.. :D