Andrewm
Tremor Fiend
I don't have a 7.3, I have the 6.7 but I think it's still applies. When I first got the truck I couldn't get better than 18mpg highway and averaged around 17mpg... I never calculated because I don't care that much. The truck now has 5k miles and I am getting about 22 or 23mpg highway and average 20 or 21mpg. So I'm thinking the truck needs to break in some. Hopefully you start to see 12mpg or whatever the 7.3 people claim.I am having the same issue. I am just shy of 1,000 miles on the odometer. I have never achieved anything better than 8 mpg (not towing). That is calculated mpg, not the truck computer. The truck computer does indicate the same. I drive as easy as possible and use eco mode.
As soon as I reach 1,000 miles, I am going to take it to the dealership and have it checked out because there must be something wrong with the truck.
I have repeatedly checked with my scanner for any codes or issues and nothing is showing. I have also checked to be sure that the front axle is disengaging. None of the wheels get hot, so the brakes are not dragging.
I have seen here on the forum over time that a few people have posted about the same issue.
If anyone has any ideas on what is causing the low MPG, please let me know.