Toyota Repair: 2001 Camry, scantool, filter air

Question
I have a 2001 Camry - 6 cylinder with 54,300 miles on it.  The check engine light came on and it started to idle rough and be sluggish up to 40 mph.  After 40 mph it picked up.  I had the codes pulled on it and it was P0300. We have replaced the spark plugs which fixed the idle, replaced the fuel filter & air filter.  That seemed to help and took the check engine light off for a day but it came on again.  It is still running sluggish up to 40 mph and now seems to be misfiring while driving.  Any other suggestions on how to fix this ?  I have had no other problems with this car.  Is it possible that if I have gotten some bad gas that it would cause these problems ?

Answer
There is a common problem with the ignition coil packs, there are three of them located on the left bank
(#2,4,6),each one fires 2 spark plugs, you need to find out which one of them is misfiring, the best way to locate the misfire is with a scantool so I would recommend having either the dealer or a competent repair shop diagnose it further to see which one of the coils is causing the misfire.