Its a fluid that help
Its a fluid that help decrease emissions and increases fuil economy. I'm not sure if its the DEF or if the truck is just that efficient but you dont even smell the diesel exhaust. Secondly if you buy any new diesel truck it will have DEF, I believe its government mandated.
As for towing the truck it rated for just over 9'500 lbs. My buddy told me it towed the 8'000 with ease. However if you plan on towing that much often I would recommend the 2500. In my opinion any of the 1500 trucks are great for day to day travel, loading the back end with normal house waist, the weekly Home Dept run, or towing your boat occasionally to the lake. I know there are people that do it, but my opinion is that 1500 truck are too small to tow that much daily.