I have 2001 GP GT so 3.8L NA. Currently getting 24.5 MPG which is up from 23.1 i was getting before I installed K&N Air Intake and Throttle Body Spacer. Car has 217,000 kilometers (135,000 miles) on it and I have just started running one tank of Premium every (3rd) month to see if that makes any difference. Daily Driver 50-50 City and Highway, I rarely let get empty, but I have got 320 miles on a tank with some still in the tank (light was just coming on when I pulled into the gas station).