yeah, $50 code reader or slip on down to vato zone and have them read 'em for free.
most likely #3 or #4 coil has had antifreeze dripping on it and it's dead OR the plug has blown all the way out.
telltail sign is the coil is broken...
if the plugs blown out, haul it to a shop with the correct tool for installing the correct insert.
You dont need to scan the codes, Like Tom said just replace the coil pack on the back hole passengers side. Its the one that goes bad on those trucks because condensation leaks off the A/C parts above it (or coolant from the heater hoses) and kills it, then they start to miss. Word to the wise, use an original Ford coil pack because all the aftermarket ones suck ass.
If you replace the back one and it still misses, put the old coil pack on the one in front of it.