Fuel filters that are not problamatic yet but still more restrictive than they should be can pull the fuel milage down a little as well. No scientific proof but a few owners over the years did mention they noticed the fuel milage was somewhat better after a fuel filter change. Probably where the owners that are pretty anal at keepng an almost constant check on their fuel milage reported this.

At first I thought this was not too logical but decided the partial obstruction was probably lowering the fuel pressure in the base of the injection pump. Perhaps changing the equality of the power balance across the engine.

I also believe that a little more air pressure in tires than sugggested hurts ride quality a little but really reduces rolling resistance. This may also be a little dependant on the tire stifness from a design and manufacturing perspective.