i thought lumina only went up to 1999 - do you have the lumina apv or the lumina sedan? I have the sedan. We might be talking different things, you would naturally get less gas mileage in a minivan.
i had also cleaned the throttle body and surrounding intake parts when i replaced my intake gasket. Still getting 30mpg (well right at 29.8)... (I use a/c all the time now) still same driving patterns (65-70mph interstate most of the time, non-congested traffic conditions)