ya being in sixth gear at 35mph wont give you the greatest gas mileage, for 35mph i prefer fourth sometimes third(i feel safer having a little rpm, it would allow me to maneuver the car a lot faster in an emergency is all..i live in utah lol i'm a very defensive driver)
i pretty much race my car around all day, maybe not rallying it but 6k on the tach isn't uncommon, and i still manage about 22-23mpg in town. and I drove down to st. george from SLC and got 27mpg...i was satisfied lol (yippy)
but as far as trying to get the best mileage goes..check the owners manual. they have recommended shift points(in mph, not rpm's) for "accelerating" and seperate shift points for "economy" driving. so check it out if your really getting that bad of mileage...19 (boom04) thats terrible!