Mark makes a good point about the plugs, that coupled with the fact that YOU feel the replacement is suspect, then I have to agree that it may be a good idea to swap them out.
Still I would look for a vacuum leak before changing the number 1 plug. The #3, and #6 are easy enough to get to.
Also you might want to start considering a compression test.
__________________
BroncoJoe19
2006 Alt Fuel Jeep (electric)
'98 windstar 3.8L
'99 Crown Vic 4.6L
'90 Full Size Bronco 5.0L
I'm not a professional mechanic, take my suggestions with a grain of salt, or a cup of coffee 
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