symptoms of clogged fuel filter would be loss of acceleration, or even may act as mph limiter. i suppose you might not know the former if it's been doing this since you got it.

check your plugs for carbon deposits. if so may be running rich. while your at it, do a compression check to make sure all cyl are withing at most 10% of one another. bent valves may let gas right back out...

what kind of mileage are we talking. I get about 24-28mpg.