Chris 
2017 Nissan Titan XD Diesel SL 4dr Crew Cab SB (5.0L 8cyl Turbodiesel 6A)
Problem with the milage computer
 This appears to be an unquie problem. I can average between 18 to 20 miles per gallon when the milage computer is not malfunctioning. Periodically it will show I am averaging 5 to 7 miles per gallon. I did video tape the instrument panel when the milage indicator was acting up and when it is fine to prove the am not driving rough.  I was able to convince the mechanics at Car Max it does have a problem they cannot figure out.  I took it to Nissan 1st and I they told me everything was fine, it must be the he way I am driving. I have not shared the video with Nissan yet. It acts up about 25% of the time.  Due to the problem the milage indictator averages 14 MPG.