Chevrolet Repair: 2002 Chevy Impala 3.4L 109000 miles, chevy impala, check battery

Question
I replaced my spark plugs and wires 10/01/06. I now have 2 misfires. This has happened two times before. What could make my spark plugs go out so quickly? They are suppose to last 50,000 miles.  

Answer
systematicly check the electrical system, starting with the plugs,  then wires, then so on back . check battery, ground, etc.  could be that there isnt enuff juice getting put to the plugs and thus cuasing a short.  are you getin grough starts? idles? etc??
something is causing your plugs to go bad in a series of months.  what kinda of plugs are they? chep ones? or the high quailty ones? i reccomend the high quailty ones.
doubel check and check....