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Welcome to the forum.
People have done those mods (except maybe the vent one -- does your car not already have a vent setting?)
Bummer about the new tires dropping MPG. That's normal, even if you stick to the same tire (deeper tread = more losses).
I'd start by adding instrumentation if you haven't already. Driving style has the single biggest impact on consumption, and feedback is the way to fine-tune it.
Since you've got the HX, you really need an MPGuino for accuracy. (OBD-II tools don't properly calculate fuel consumption when you're in lean burn mode, but the MPGuino does.)
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