You need to watch the 02 sensors on the live data stream, a code may or may not be set by a contaminated 02 sensor. The upstream one is the only one that matters. It could dump up to %25 extra fuel before the code is triggered, more than about %5-%10 usually means something is getting skewed.

Avoid the snake oil at the parts store for cleaning injectors, just try a couple tanks of premium fuel from a tier 1 supplier, they have way more cleaner than normal gasoline and since the engineers supplied it already mixed they probably knew what they were doing better than someone bottling acetone in their basement.

I am not sure about the 05 but early 4.7 had a single squirt hole in the injector, a swap to some ferd 4.6 infectors usually nets a little better MPG as they atomize the fuel better, if your swapping injectors anyhow.

A car usually gets significantly worse MPG in the winter because fuel is not evaporated as good. Gear oil gets thick and hard to stir, oil gets thick, PS fluid gets thick, trans fluid gets thick...

Alcohol content usually goes down in winter because it don't evaporate as good and hinders cold start a hair, of course E-85 never really made my cars hard to start but that is what the fuel makers say.