Could be, and it may not be.... but for $10, it's an easy cheap fix attempt - and you said you haven't replaced it, so it's a good start.
One thing to keep in mind though, if it is a firing issue, where a cylinder isn't firing. This can potentially damage the CAT-Conv'....fuel from the mis-firing cylinder is ejected into the exhaust, which makes into CAT - causing it to burn there creating extreme heat in the CAT which can damage it.
So you may want to seek professional help soon.
GO BABY GO! 
