I get about 41.5mpg highway with 2 adults and light cargo in the summertime with my LX wagon, and I haven´t tested my GT yet but the previous owner said it got about 34-36mpg highway. Right now, in the winter, and the way I drive, I´m probably getting about 20mpg or so.
Check your o2 sensor, idle speed, and VAF... sounds like you´re running really rich.