I have a 2002 Expedition, probably same motor (5.4 V8). I have experienced the exact symptoms.

As mentioned above, the coils are notorious and I have had to replace several. The good news is that that they're fairly easy to get to as they're located on top of each spark plug. Diagnostic (from the dealer?) will tell you if that's the problem. Bad news - if the dealer does the repair they're expensive.

Longer method, but much less than the dealer will charge, is to buy a new coil and begin substituting until the problem goes away.

Good Luck,
Glenn