Awful Mileage?

Of course, (i moused over your name and got your transmission) the manual is the only way to go. On the new ones they advertise that the 5 speed auto (such as it is, horrible reviews) gets better gas mileage. But its hard to save gas on an automatic. Its always automatically driving for you. If you had had "auto" in your name, I would have figured you a fool for even trying to get better gas mileage (out of a 98) and ignored it.

ya start getting up in mileage and you start losing tolerance all over the vehicle. Sometimes it makes it loose, sometimes it makes it more binding. Compression might be slipping at that mileage too. Bet if you got a top end and injector cleaning done on it, you'd notice it. I'm not familiar with your tires, but some have horrible rolling resistance which isn't obvious to the eye.

Also I was getting better mileage than that at 50k using fossil fuels. If your area is using 10% E then you're going to see a few percent drop vs 10 years ago. Are you using the recommended oil? (10-30 in 98?).

Yea you're not in worrying territory. But we all want to save money, the planet, and still drive what we want/need.
keep up on your maintenance...