I have a 2000 Excusion 7.3, automatic and factory stock. The overhead computer showed I was averaging 11 mpg. I thought it was low, so I had checked for leaks, replaced the filters, took it to the dealer twice for inspections, and was told it was within factory specs. Still, I wanted to chase the 15-17mpg I read about! I added a AFE stage 2 intake, 4" Magnaflow SS exhaust, Edge Evolution tuner, double and triple check everything again. I set it to 60hp econo/tow. I the drove 200 easy highway miles, keeping it below 60mph and under 2000 rpm at all times. The overhead computer showed 23 mpg!!! I was happy until I actually verified it at fill up time, when I discovered I really got 13.5 mpg. Taking into consideration it is a big, heavy vehicle, I suppose it is not all that bad. If it was gas, I would be getting only 8.5 mpg.