Mpg dropping

I used to drive a truck like that for my employer and I thought 10 mpg was about right. Now if the mileage dropped suddenly, maybe you should watch for a check engine light or have the fault codes scanned anyway just to see if something might need serviced. On a related not my Ford Taurus suddenly went from 27 mpg up to 30 mpg and I had just bought gas far from home where the gas is blended differently. I'm thinking less alcohol helped my car gain 10% and it dropped again buying gas near home again. So your mileage loss might be alcohol related and nothing serious. Another factor, pulling trailers, wind resistance is a big factor. A strong wind can hurt or help mileage too.

I use tow and haul button and get same mileage whether I'm pulling trailer or not. Mileage has dropped in last two weeks from 11.5 to 9.6 have gotten gas all over the state

10 mpg on a dually used for work is not that bad. I assume you are running the diesel. If so your engine may have gone into a regen cycle for the DPF. Check your oil level, if it is going up you have a problem with excess fuel dumping into the engine.

Nope truck is gas not diesel and no dummy lights have even flickered

Ran scan nothing shows up not even time for next oil change

Did your state just change fuel formulations? Make sure the air filter is clean and check your tire pressure.

If you can get 100% real gas use that as E10 or E15 will reduce your fuel economy.

Tire pressure is checked daily. Air filter is CLEAN as a whistle. Maintenance is done regularly because of pulling trailer, probably more often than most. But I think Ohio did just change something about gas mixtures. Will have to double check that.