It has been my experiance that you can start in a couple of
places.  First, make sure you are using the correct plugs -
not Bosch!  Check for vacuum leaks.  One of the more common
causes is a bad EVP sensor which usually will not set a
fault code until it is plumb off the scale.  At low rpm and
light/moderate load, the ECM opens the EGR until it senses
it is open far enough.  The problem is a low/slow reading
EVP sensor is not producing a full signal which causes the
ECM to open the EGR too far making the mixture too diluted
with exhaust gases in that range resulting in a misfire.
Your ECM cannot record or sense a misfire and usually cannot
recognize a bad EVP sensor signal.   Also, make sure you
check the #7&8 plug wires to make sure they are at least 1"
apart at all points if you have the 5.0L V8.  There was a
TSB on that years ago.