Hey there!
I have an 05 STX 3.0L
Ive been having misfire problems on cyl 3, about a month ago it became really noticeable, I replaced the plugs and coils (the plugs looked fine but I replaced them anyway), and the problem went away for about a month until earlier this week I was driving and lost power/acceleration. threw the same code, misfire cylinder 3. Gaskets are all fine, I ran a compression test and everything was okay. I havent pulled the plug yet because I dont think thats the problem.
Im stuck between 2 ideas: (I hope its this one) Bad Gas/water in the gas.
or: Ive always had a CEL for an o2 sensor but never really did anything about it because I was just being lazy. Now I'm worried its the cat system. Im fairly certain this is the problem because it does sputter a bit on idle... no sulfury smells or smoke from the exhaust thought. I haven't checked temp of the cats yet because work has been a busy week for me.

If it ends up being the cat system does anyone have any good recommendations for a cheaper cat? Id rather get a ranger/model specific one rather than a universal to save myself some trouble, bolt on is better.

Or my other idea is cutting the cat system out and straight piping the truck and using MIL eliminators to clear the codes and very hopefully pass emissions...

any or all help is appreciated

 

how many miles on the motor? did you ever change the O2 sensors?