Just like these guys are saying there is really no reason to freak out. You will start to notice some improvements near 3k miles or so. When I got my car it had over a 400mi range. When I drove it for a while the range went down to under 390 after the first few weeks. A month or so ago I had the range back to over 400mi/tank. Since then we have switched to winter blend and I am getting 394mi/tank. It really depends on how you drive and conditions around you. We have a lot of construction going on right now and the highway sucks so I am getting less than what I used to. I used to get about 24mpg or better going to or from work. Now I'm happy if I can get 22. I also use a premium fuel (not to be confused with premium grade 91 fuel) from Shell. Whether or not you subscribe to that is up to you (ie using "premium" fuel from places such as shell, BP, etc... and not using it from cheap gas like Marathon, Gas America, Walmart [Murphy], etc...). Also be aware aware if you have an Ethanol rating at your pump and how much it is. I believe EPA tests are run on pure gasoline, most consumer pumps have E10 (10% ethanol), you can thank our wonderful federal govt. for that bit. There are possibly places near you that do provide pure gas (slightly more expensive just as E85 is less expensive due to less actual gasoline), you should be able to find those at
Ethanol-free gas stations in the U.S. and Canada