MPG's NOT where they should be

[brandonl2000]

I have been getting 17ish mpg driving approximately half and half city and highway. This is a problem since I'm a GT; I should be seeing 21mpg at least.
No SES lights are on, just did the LIM gaskets, new coolant elbows, new air filter, fresh oil change, and cleaned plugs*.

The car is running great with no misfires that I can tell. *However, the first time we did LIM gaskets, the plugs fouled twice. We cleaned them with brake cleaner and burned it off. They are basically new Delco plugs aside from them fouling twice. Could this be the culprit to my MPGs or does it even matter?

Also, I have not changed the fuel filter, mainly because IDK how to do so on this car.

So, any feedback is great. Just looking for what could be affecting my MPGs and what else I could do to help. Tonight, I checked all the tire pressure and each tire was about 10-15 PSI too low. I haven't drove it long enough to get an accurate reading yet.

Thanks!

[noreasonwhyy]

you should probably check tire pressure when you check fluids, as that was likely your problem.

safety and fuel economy are reason enough for me to check everything out at least once a week. gas is up to $3/gal again. bastards.

[brandonl2000]

yea, i just checked the tire pressure tonight so hopefully ill see a difference tomorrow. they were definitely 10-15 PSI too low.