I think it was a development engine that the Dirt EVery day guys used in that video.... That being said, The 2017 Titan now has a Diesel in it.
To the original poster, you have failed to include details that are relevant and prevent us from really helping or confirming what you suspect.
Some great info would be... Tire size, any mods done to the truck, are you doing maintenance on it regularly or just beating on it and *****ing about unknown factors????
For reference. My 2013 got 21 MPG pretty much no matter what I did and as long as I loaded less than 600 pounds in the bed. On rare occasions I would get more but I could plan on no less than 21 MPG. I switched tires lately and put a lift on. I knew I was going to get worse mileage and honestly its a little worse than I hoped for but the things we do for a cool looking truck. I dropped to about 17 mpg with a simple change of 285/75-16 tires, so I understand your concerns a bit. Now having said that, you can look at things to improve, such as tire size, driving style, etc etc, but we can't help if we are guessing stuff all the time.
FWIW I will be swapping back to a 265/75-16 to get some mpg's back in the not too distant future but I am in no huge rush right now and the only reason I am OK with that is becuase I have another project truck that I'll swap the larger tires on to and I will probably never really care what kind of mileage I get out of that truck because it's my Zero f**ks truck and it gets a pass as long as its got the power to do what I want it to.