Originally Posted by FuzzFace2

What I meant was if going by the mileage on the gauge it is not right with the 31.5" tires, just like the speed reading being off.

Lets see if I get this right so bear with me.
You have a taller tire on the truck, IIRC it will slow the speedo & less mileage for the speed & miles driven.
You may show say 50 MPH but you are only doing 45 MPH and for every mile driven may only show say .75 miles on the gauge.
Again I am only using the numbers to show what could be happening and why you need to make sure the speed & mileage on the gauge is what you are doing.

Your 197 miles may be say 230 miles on the 18.6 gallons. that would be only 12.37 MPG (230 / 18.6 = 12.365) still not good but better than the 10.5 you got.
So you need to check the gauge to make sure it is right and get them codes fixed.

As for the 14 - 15 MPG in the city dream on, I can just get 15 MPG doing high way 70 MPH and back roads at 45 to 50 MPH and I dont have a 4x4.
Do you have a tach in the truck and if so when on the high way what is it reading and at what speed?
It could be you are way below the motors sweet spot, I want to say mine is around 1800 RPM or a little more.
Dave ----

Originally Posted by Old Guy F-250

Hey Subzerospeed,,,
As I read all your posts it is hard for me to figure why someone would be asking about bad mileage WHEN you pretty much have your own answers.
Looks like You need to spend more time checking what you have and fixing problems BEFORE asking questions.
These guys on here are a GREAT source of information BUT it is hard for them to answer questions when you have not done your homework first. (how many converters on my truck) get under there and look.
You have codes up the _____ and not sure of your mileage and asking these guys on here why you have bad mileage???
I think everyone here is always willing to give great advice but we probably should help ourselves first.
Have all codes cleaned up, know exactly your mileage, then if your gas mileage is what you think is bad ask for input and ideas. You will then receive excellent ideas of what the problem may be.....
My .02 worth..