P0300 With Looping, Mis At Idle, Lean

[wdavrac]

Keep getting the P0300 code in my 05 sierra 5.3, 80k mi along with an annoying loop/misfire that you can feel while sitting at a light not consistent though, all else seems fine and no real lack of power. Maybe more fuel consumption, and ablack soot on tailpipes Need ideas!!!

 

Changed

plugs, wires, intake manifold gasket (two yrs. ago it acted similar to this took it to dealer and they said it was that and replaced it,and all was well, guess I freaked and assumed it was that again and changed it, most likely wasnt it. Had the teal gaskets, and my replacements were carquest victors with the orange, either way no change in engine or code.)

 

Also the morning I changed the plugs I ran the engine for about 5 mins prior, was sitting in 10 degree garage, pulled plugs and they were reddish orange all around???

 

And last, if you add aftermarket exhaust do you have to reprogram anything?

 

Thanks

Dave