Very low gas mileage

We have a 2005 Saturn ION2, 2.2, auto, 17500miles.
Since new best highway mileage is 26 mpg. In town is 16 mpg. Back to dealer many times and always says that computer is saying that it is getting 37mpg. Talked to other saturn owners with same auto and their mileage is 26-28 city and 35-39 hwy. How can I get dealer to take care of this problem. Writting Saturn co and I get boilerplate letter that they stand behind dealer. Other than jumping up and down in show room and scaring away potential customers what can I do.