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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sharkman:
Have you done anything to your vehicle? What speeds do you drive?

I added a K&N filter and a flowmaster exhaust (both are supposed to improve the gas mileage). Also, I have the roof marker lamps, a brush card w/ PIAA lights attached and the luggage rack. </div></BLOCKQUOTE>

Marker lamps MIGHT cut down on some fuel economy since it is a wind restriction, but not that much.
Here is a thread I submitted last week on my fuel mileage I recorded on a trip. Vehicle had less than 1K when I left, and had only about 2200 when I returned. I expect it to go up as the engine breaks it, maximizing around 4-5K on the odometer.
The only speed limit I know is one where I drive safely, not what is posted. Average speed was around 73 mph per my GPS, but I hit 85 a few times, and I-65 through KY is not flat, especially when coming out of Louisville.
TN, believe it or not, is downhill out of KY, but still some rolling hills. Also some traffic through the larger cities.
As for the filter; K&N makes a lot of statements, and I never checked fuel mileage with one, but I can tell you from dyno'ing a Vette (and a few other Vettes on the same day owned by other people), K&N's statement about increased HP is BS.
As for exhaust, there is not that much restriction in the newer mufflers, and if all you did was setup to the rear of the resonator and the cat, you will not see much in the way of fuel economy over a stock muffler, and no increase in HP.
In the olden days, when mufflers were more restrictive, I would say a cat-back was a good investment. Now, it is more for looks and sound; and there is nothing wrong with that.
Good luck, and I sure hope you get your mileage figured out by a dealer.