My 2001 with the 5.4L does this too and I too have been told that this is normal. It almost acts like a lean condition, it has a flutter in it that can be felt in the truck.
It runs fine other than that. I am assuming that it is set up to run lean for emmisions reasons. My 5.0 Mustang has also done this since it was new. The dealer tried to tell me it was because of the big HO camshaft. It still does it @ 156,000 miles and hasn't hurt a thing.
Jimmy