I have noticed recently that my engine has been making a semi audible knock when running, not just when cold. At first it was from the passenger side and I thought "OK it is just the chain tensioners going bad". Well it has been about a week and the knock is now on both sides, and my DPFE(only has about 1K miles on it, it was replaced recently) might be going bad again with a P0401 code being pulled. The truck doesn't seem to lurch, but when I am at about 60mph and let off the gas, you can feel something like a hard downshift, and it slows down like 2MPH. Then it normally decreases another 3 MPH and then does the downshift lurch again and gets to around 54MPH, does it maybe 1 more time much more lightly, and then doesn't seem to do it at all. It has only started happening since the knocking has been occurring. Another thing that may have something to do with it is that there was a tiny bit of smoke coming from under/behind(towards the passenger seat) the battery one day, so I pulled out the battery and the housing for it, looked, but didn't see anything that looked too bad. I have been checking for leaks and do not see anything, my oil level is fine and was changed about a month ago with what I believe was a motorcraft filter, not some FRAM. The guy who did the oil change(free of charge) almost always does the oil change which is why I believe he used a motorcraft. My mileage also went down from around 10MPG to around 8MPG. If anyone need any more info, just ask

Edit - I didn't really know the symptoms of a blown plug, but recently it has been raining a lot and I have been doing some small time wheeling, so I have been revving it much higher than normal(about 3500RPM tops when in the mud). Do you think I could have blown a plug or 2?