I have an '06 F150 4x4 crewcab with the triton v8-85,000 miles. After traveling at highway speeds and then moving to side streets and traveling steadily at approx 35 mph or 1300 rpm, when I accelerate I feel a stutter or thunk. I changed the oil and additive in the rear diff (I had an issue with the diff when it was still under warranty and this thunk feels like that). Diff oil change didn't help. Changed tranny oil and filter - that didn't help. I believe the transmission is in overdrive when I accelerate at 1300 rpm and tries to shift down. Not sure if it's a computer problem or what. I appreciate any advice.
Might try running the truck with OD off and see if you get the same results. I had a similar problem and it turned out to be a bad coil. Changed the coil and it was fixed. Might also check spark plugs as well.
I had the similar problem and it got worse by the week. Did Transmisson flush and fuel filter change with no help. Finally got it in the dealer and they changed all the spark plugs and tested all cop before re-installing them. The problem seems to be gone. I need few more days of driving to confirm it is really fix the stutter problem.
The truck has 100K km on it and was told that all plugs came out in one piece.