Ya the 99' GT I just got a few weeks ago was geting about 17-18mpg. The plugs were good, but the air filter and oil was nasty. Changed them, threw in some Lucas Oil injector cleaner and it bumped up to 20 mpg. Still wasnt good enough for me.
So I took the air intake off, and looked inside the Intake and it was pitch black with carbon deposits.
Took some good TB cleaner and sprayed it into the intake/TB with it running 4-5 times really good(you hav to throttle up for this, kinda loud too!) , the last tank after this cleaning was 24mpg. So apearently that was my problem with my bad mpg.
Also keeping your oil changed at regular intervals helps big time too.
Just though I'd through in my
