How do you all get 6.2s to 300K miles

[nycxjeremyy]

Cylinder seems to be missing ? ? ? ?
Crack loose one injection line at time, its like pulling plug wires onna gas enjun.
Any leak on the injection line system will cause rough running.

Missing?

 

[MrMarty51]

Missing?

Yes.
If an injector line begins to leak it will cause that cylinder to miss.
If the leak is not too bad the cylinder will begin to sort of drop out.
If there is a bad injector, or for some reason the engine has a miss, start loosening the tube nuts at each injector, usually a couple of turns, if the line does not break seal in a couple or three turns of the line nut, gently tap it with something like tue wood handle of a ball peen hammer until it breaks seal. That leaking injector should cause the engine to miss, tighten that nut back down and move to the next cylinder, repeat until You come to the cylinder that when the line nut is loosed and the seal is broke so that line is leaking and that cylinder makes no difference in how the engine is idling, that will be the dead hole.
Swap that injector with one from a hole that is firing good and if the miss moves to the other hole then replace that injector.

 

[Will L.]

Not sure if its just a placebo affect or not, but ever since I tightened those leaking fittings on the IP, it hasnt smoked the way it has, heck, it even starts smoother now

Not placebo. All those symptoms are right in line with the line being loose.