I'm running a tune from 5 Star and my 02 V10 gets about 8mpg city and 10hwy no matter what. I do have 4.56 gears and 35s so I'm not too concerned about the economy to begin with!
Scott
Maybe I'm asking for too much or just plain dreaming then! Mine's geared 3.73. Getting 10mpg city.
Gas milage dropped to 9.88 at one point, so I took it in to dealer. They detected EGR valve tube loose at exhaust. After an involved repair, gas mileage has improved significantly.