this may be a longshot...but my average for mainly highway driving is in the 14s, so 13 doesn't sound so bad in city driving. this is on a '97 3.2l with automatic and 265s. i don't know how it is in your area, but i've been convinced that bad gas was hurting my vehicles. it started with the trooper. it sounded like it was rattling more when i was using cheap/sams club gas. it improved after some techron and a switch to chevron and shell gas. then, my wife's minivan's check engine light also started coming on, but cleared when i "asked" her to start using chevron or shell gas. i recently came across an article about top tier gas, which talked about how certain companies have not cut back on their fuels' detergent levels while others have. i don't know if this is fluff, but it's just a thought. good luck.