I have a 2008 f150 4x4 with the 5.4 and 67,000 miles on it. About a month ago my truck started misfiring when I pulled up to a stop sign or redlight ever now and then Probably every few days. It was sputtering really bad so I would turn off the engine and when I started it up it was fine. Never threw and codes and still havent to this day. So, I took it to the dealer and they said I had a misfire code and recommended I change my plugs. They changed the plugs and since then the truck hasnt done that again but now there seems to be some hesitation or feels kind of like an exhaust valve leak all the time. Before the plug change I was getting 15.5-16 mpg and now getting around 12.5-13mpg. Took it back to the dealer and they said everything checks out. I asked them to test drive it with me and they felt the noise I was talking about but said it was nothing but couldnt explain the loss in mileage. Has anyone ever had something like this happen? Not sure what to do next? Is there a good Ford mechanic in the Dallas Tx area that I can take this to and get checked out? Not sure I trust the dealer anymore. I should also not that it is still under the 7 year 100,000 warrenty.