We're getting on average 20 miles per gallon in the'05 TL for an 80 mile daily round trip journey. These are 99%freeways miles and she drives between 70-80 mph

I have done a couple of experiments where I top it up to the brim with gas, she does a round trip to work and back and then I fill it up again.

Do I have a problem? I normally take the suggested EPA quoted values with a grain of salt, but about 50% off is a bit too much. Any sugestions would be appreciated.
Thanks Sujit