Ive got an '04 4.0 with an auto trans. 48K on the clock. Just the other day I was cruising between 50-60mph and I heard a loud thump and my truck kind of shook like I ran something over....looked in the mirror,didnt see anything so I figured it was a pothole. Couple miles later it happened again and continued happening anywhere from every 2-5 miles. WTF, transmission shifts fine everywhere, no noise, vibrations or anything and it only happens between 50-65mph. I went home, checked the trans fluid it was just above the bottom of the hatching so I added a little, right around the top of the hatch now and it seems to be doing it less (I think) there seems to be no pattern to it or related to anything I am doing with the brakes or throttle, it happens less now but did it once on my way to work this AM. I plan on bringing it to the stealership because I still have a powertrain warranty but that ONLY covers internals on the trans and engine....if its something different I dont want to pay their rediculous rates to get it done. Anybody have any ideas?