Misfiring 2015 GMC 3500HD

[darren,smith]

GMC Sierra 3500 HD 

Codes shown as catalytic operating below efficiency.

Replaced both Cats and all 4 Oxygen sensors...now its misfiring.

Replaced Battery, ran great for the night...then started misfiring again the next morning.

Replaced Camshaft Position sensor...Ran great for 30 min on freeway, sat for 2 hours and started to misfire again....

 

Im at a loss....any hints?

[2016HD]

Missfire.. When did you last replace the spark plugs? Plug wires or inspected the coil packs?  Thats where Id look first.  Then possibly injector harness issues or fuel issues. 

 

 

[CamGTP]

Figure out what cylinders are misfiring. Then go from there.