I have the same thing happening to my 2001 F150 5.4L with 122k on the clock but only after she sits for a few days and it has been humid or rainy....
Hate to start the coil hunt and figure I might as well replace all 8 at this point!
Informative thread.

is this the right one?
Alternate/OEM Part Number(s): 3W7Z12029AA
MOTORCRAFT Part # DG508
$41.79 at Rock Auto