Driving speed mainly. A very large amount of my driving is on secondary roads with high deer population so I usually drive 40-45 MPH range with c/c set on them. I do very little driving in town too. I also added an electronic throttle controller in 12/19 and have it set to economy mode. I do lots of coasting to stop signs and toward upcoming red lights trying to give them a chance to turn green prior to getting to them and having to stop. These mileages were achieved using 15 year old conventional 10w40 Citgo Supergard and 87 octane E/10 for fuel. No one is going to convince me you have to use 0w8 to get good mileage. I guess it helps that I'm an old man and drive like one!