Gas milage issues, now I'm stuck.

[nextse7en]

All questions pertain to a 1992 USDM SVX.

My SVX has never gotten very good milage - at one point I was lucky to see 10 mpg

In an attempt to fix this problem, I have replaced my 02 sensors, and replaced all vacuum lines and EGR related tubing under the intake plenum with new material.

This has helped in a moderate way, I now see 18mpg on the Hwy, and about 12 in town. I drive with a moderately heavy foot.

Could someone assist me in next steps in my diagnosis of this problem? Knock sensors, maf cleaning?

There is no other indication of problems - drivability is excellent, and there is no CEL illumination.

Thanks,
Patrick