Where to start?
Regular unleaded gas is getting harder to find. Your best bet would be a station near a lake or campground. It'***** or miss on whether you can find one though.
Traction control is there to help save you from yourself, for the most part. It acts as a sort of limited slip. It applies some braking force to a spinning tire to attempt to force torque to the opposite tire. You are most likely to see in in wet or snowy/icy conditions. You will probably rarely see it for normal driving. Turning it off shouldn't affect your fuel consumption.
In the winter time, the fuel blend changes and you will also see a drop in mileage. Consider that the engine adds extra fuel until the engine warms up. It's not unheard of to lose a couple of MPG in the colder winter months.
I would actually recommend against tires branded as "fuel efficient". To improve the fuel mileage, they reduce the traction that the tire has. Works ok in dry climates, but are almost as bad as summer performance tires in snow and colder temps. When I had said to reconsider your tire choice, I was referring to heavier aftermarket wheels and the bigger offroad-ish tires that people like to put on their non-offroad SUVs. Tire/wheel combination can change your mpg by 1 or more.
Chemical treatment can help, if there is an issue such as dirty injectors or carbon buildup in the cylinders. Depending on the extent, over the counter cleaners will only scratch at the surface. I usually recommend a cleaner additive every other month or so. Just a bottle added to a full tank to help minimize buildup. Especially if you run the cheapest 87 octane that you can find. Each state seems to have its own requirements for fuel additives from the refineries, so in many cases the additional additive is unnecessary, but I haven't found any evidence that a little extra hurts.
You've tried a few things, and run some cleaners through your tank. Unless there is/was a failed component, there isn't a silver bullet fix that will instantly give you the mpg that you want. Drive it around for a bit, let the cleaners work and allow the ECU some miles to readjust the fuel trims.
