My 2001 F150 4.6L misses under load. There's no computer
record and the dealer can find nothing wrong.
A miss under load conditions is often the result of an insulation
breakdown under the higher spark plug voltage needed at high
manifold pressure. Wipe the dirt off of everything subjected to
high voltage (plugs, boots, plug wires, coils, distributors, etc.)
and inspect the parts for burning, cracking or other failure.
Sometimes you can see a voltage leak by duplicating the driving
conditions: Place the truck's front bumper against a solid wall
and have a friend run the engine under load while you look into
the engine compartment for high voltage arcing. Do this in a
totally dark area so you can see small arcs.
Wendy & John.