Well, you're in the neighborhood. I know the '98 diesel
was rated at 26 city/34 highway - you are in between
those two figures. I don't necessarily see a problem.
How do you use the car? Short trips, long trips, city,
highway, suburban? This all makes a difference.
Try using EC/economy mode on the climate control - that's
good for 1-2MPG.
I have a '98 turbodiesel. I see 25-30MPG in mixed suburban
use. Lower figure for lots of stop&go with the air
conditioner blasting, higher figure if I make a few trips
to the airport.
Road trips have netted 32-34MPG. Not up to spec, but I need
to note that I generally drive in the vicinity of 80MPH on
the open road. (No flames, I'm in Texas and things are way