I need help
 

I have a 2004 Buick lesabre limited V6. I started experiencing issues with my vehicle yesterday. It drives rough and check engine light came on blowing a code of P0300 random misfire. I changed all my spark plugs as well as wires started checking the coils for the spark plugs and found out one was bad so I replaced it this morning hoping it would do it but still nothing my car still runs rough. Is there anyone who has had this problem or that would be in assistance to me by chance I would greatly appreciate it.

Could be:
Plugged Fuel Filter
Bad Catalytic Converter

Hmm, misfire is detected by the crankshaft position sensor. Those too have failures and takes forever to find the problem, along with all the other mentionables.