This is form a guy on the TDR. Sounds like his truck is falling apart ;)
"2011 3500 rear wheel drive duelly 68RFE auto. In dash hubometor is stopped and stuck at 619,639. Fuel mileage sliding tape is with no sliding tape, average fuel mileage shows zero, trip A and trip B also stopped. Speedometer and tachometer are working good. I am thinking the output speed sensor located towards the back half of the 68RFE tranny is bad. Any experience or input on this would be greatly appreciated.
I was traveling from El Paso to Chicago, three big pick up trucks loaded on my 52 1/2 foot flatbed, glanced down and noticed I was getting zero fuel mileage. Yes I make this truck worked very hard, and yes it does have that many miles."