The wife and I almost always do *better* than EPA rated.
1997 Neon Sport...rated 24/34, the wife got 28/36 1997 Grand Caravan 3.3 V6...rated 18/24, I get 18/27, wife gets 18/24 2000 Neon SE...rating unsure, daughter gets average 31 (mixed) 2003 Stratus SE 2.7 V6...rated 20/28, Wife gets 25/29 2004 Sebring LXi 2.7 V6...rated 20/28, I get 24/31
I did have a 2003 Chevy Malibu that I hated...so I got rid of it last year after 9-months. It had a 3.1 V6 rated at 20/29, I got 19/32 (I have no idea why the city/highway mileage was so far apart in real world numbers...but was consistently so).
I don't know what my son gets on his 1996 Dakota SE V8 extended cab.
In all cases, we log the mileage on every gas receipt and calculate MPG. So we have several years of history on the older vehicles. The mileage remains about the same over time (so far)...but is a little lower city mileage in the winter.
If you _always_ do worse, I would look at driving habits/conditions Quick/abrupt starts? On the throttle up to a stop light or intersection then hard on the brakes, (vs. coasting up to it)? Mountain terrain in your area. Unusually cold weather conditions. Also, tire pressure? Roof rack (apparently can have up to a 2MPG difference in highway mileage)? Wrong viscosity oil?