It is time for winter mix fuel to appear in most northern states, too -- less dense, so you get worse milage.
We had a rash of bad (dirty) off-road fuel about six years ago in the Indiana/Kentucky/Illinois area -- I did several different analyses for people with samples of fuel with "strange stuff" in it (brass shavings, dirt) and one case were the filters didn't work well enough on some old equipment (1950's skid loader) and the engine got "sanded" with silicate dust. They were having to change filters every day or more on the new equipment, never occured to them that the old filters weren't fine enough to keep the dirt out. Rebuild time.
I just changed the filters on the 300d due to low power, my brother had the same problem this summer (45 mph up hill in the mountains in West Virginia at night in the rain....).
Peter
