| Oh no.
My car has also been getting bad gas mileage lately and it's been hands down the WORSE problem I've had to deal with. It's super hard to find. It could be anything as dumb and little as a hard-to-turn pulley or dragging brake, up to bad injectors, fuel pump, etc etc.
It could just be coincidence that it started doing this after the shop, too, but it would be hard to say that because usually it happens gradually. Maybe you have a small leak on your hose if they replaced the fuel filter?
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