I still find the whole mileage issue a bit frustrating. I have a 2000 that has never gotten better than 20, less than 14 and routinely does about 16 average. Everyone I have spoken to with a 3rd gen complains that they can't get anywhere near the mileage I get, much less 23-25! And they have tried the lower speeds, proper driving, etc. What this tells me is that the build quality for these engines (and the truck as well) is all over the chart, which I find hard to believe. I have never seen such wildly varied mileage reports on any other vehicle in my life.
Whenever I do my calculations I fill at the same station, pump and direction for the course of 5 or 6 tanks so I can get a fairly accurate average.