Well hell they need to give you the readings for all six cylinders. There is low compression, and then there is relatively lower compression.
Then there is the diagnostic trouble codes which can narrow things down.
You need to gather this data and put in it the right hands.
For right now all I can offer is that this new plugs/wire set doesn't have the right resistance and that by replacing them you went from rough idle because of worn plugs/wires to rough idle because of a new set that may not match up to what your coils put out. Not using Motorcraft replacements for these parts in particular can have quite an effect. Just search the forum for this topic!
But that's ONE possibility. CyL. #5 comp can't be that low or you couldn't say that "it runs fine but just idles rough."
In the mean time try to avoid taking your truck in to this place for an oil change, or you might be handed another "you need a whole new engine" line.