cyrnel

If you noticed a change right out of the gate then it's either placebo or a change in burn pattern from the gas chemistry. If I recall, gumout is mostly kerosene with a light carrier so it won't clean as much as cause a brief octane-boost effect. Techron is a better cleaner. I think it's still ~$10/4 at Costco.

Without major mechanical problem your driving pattern & style will have the biggest effect on mileage. Tough to know if you haven't been documenting things religiously. Take any short-term changes in mileage with salt. You might be better off just leaving things as is before selling, or try a few jobs yourself? A cheap socket/tool set plus an afteroon might be very educational... just a thought.

The diagnostic we're talking about will be free and takes about 5 minutes. Don't ask for a garage check. You just want them to dump codes & make suggestions. Pep boys is more likely to keep you captive to stack labor costs. I'd try a parts store without a shop.

BTW, $10/plugs are akin to gold plated USB cables.

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There are a vast number of people who are uninformed and heavily propagandized, but fundamentally decent. The propaganda that inundates them is effective when unchallenged, but much of it goes only skin deep. If they can be brought to raise questions and apply their decent instincts and basic intelligence, many people quickly escape the confines of the doctrinal system and are willing to do something to help others who are really suffering and oppressed." -Manufacturing Consent: Noam Chomsky and the Media, p. 195