GMC Repair: Duramax Smoking again, gmc sierra, air charger

Question
I have an 03 GMC Sierra with 6.6 Duramax. Injecters were replaced under warranty at 80k miles as engine would smoke espesially wlile ideling. Engine now has 125k miles and is smoking same as before. Dealer said injectors are fine and now the glow plugs and control module are bad. $840. later, the engine still smokes as before. Blue nasty stinking smoke. Truck runs fine and burns no oil.

Answer
Hi
LB7 engine code I would HIGHLY suspect 1 of the injectors.
I have recently run into repalcing injectors and getting 1 or 2 bad replacement injectors.
Also if the copper seal was not installed, or it the hold down was not torqued.
They should be able to watch the balancing rates and pinpoint exact one. (-4 to +4mm3) is specs.
Anyone out of range should be HIGHLY suspected.
Have them check CAC (Cold Air Charger)blue tubes for proper
installation (maybe one fell off or backed off?)

For you I would check air filter. Replace if needed.
If you have an Oil charged air filter (K&N, etc...) they can cause similar problems.
I Hope this helps
Pawl