I would replace the fuel filter --- then cut the old filter open to see if it shows contamination. (Do not tell the dealer that there may be dirt in the fuel tank-- they will not repair the fuel system then)
How much turbo boost is it showing-- These engines need boost to make power! (You may have a loose inlet boot, or ??)
Check the fuel injector pressure.
Are there any codes stored?
Clean the MAF sensor.
Hope this helps.
Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.