gas mileage for 97 civic ex

I just purchased a 97 civic ex with an automatic transmission with 85000 miles. The car runs great, shifts very smoothly but it only gets 23 miles
per gallon on the highway. Anyone out there have any idea why? The tires are properly inflated, cosistently drive around 75 miles per hour (same habits as with my old civic ex and it did much better.
Tia,
Mike
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try changing new spark plugs, spark plug wires, distributor cap and rotor, air filter, pcv valve, fuel filter

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It doesn't have a distributor cap or rotor!

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Is the automatic tranny shifting to overdrive ? That'll do it.
My daughter's 97 EX manual at 75 in 5th runs about 3500 rpm (if I remember correctly).
Lynn
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23mpg is terrible, even with oxygenated gas, cold weather and 75mph.
How is this mileage being determined? Is there a certainty that it is being calcuated correctly?
Any error codes stored in the ECU?
--
TeGGeR

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