For the Duramax crowd they say keep the rpm's down below 2000 helps mileage. The other thing is the MAF sensor. I think it stands for mass air flow. The sensor sits right on top of the large tube coming from the air filter. They recommend cleaning these every ten thousand miles or so. This is also key to getting the best mileage. First head down to the local auto parts store and pick up some CRC MAF sensor cleaner. It's in spray can near the brake clean etc. Open your hood and look for the sensor on the large tube coming from the air cleaner. It had two # 15 torx screws holding in in place. Unplug the wire harness remove the two screws and lift the sensor out. Give it short bursts of the cleaner taking care not to turn it into a popsicle. The cleaner drys fast when it's completely dry reinstall, and wala your done. This is said to keep your mileage at it's peek. Anyone using K&N filters be careful about over oiling them as this can effect the MAF sensor. :smile
D.D.
D.D.