2010 Ford Fusion Hybrid

My wife and I have been generaly pleased with our hybrid since we bought it new in September 2009. Lately though we've noticed the mpg is running lower than expected. For an extended period we were averaging 40 mpg. In the last few months we have been getting 34-35 mpg. Driving habits have not really changed, that is, we have mixed driving of city and highway in the Washington, DC area. Before we take our car back to the dealer, we just wanted to check on this forum to see what other 2010 Fusion Hybrid owners have been experiencing with mpg. Your replies will be sincerely appreciated. Thank you!!!