On the LLY engine-- when a injector looses contact, it will go into "Limp" and and set codes. Just like you have-- The Power control module will sense the problem and include all injectors in group A, or group B, what ever the bad injector is on. It will be on 4 cylinders -- runs-- although not very well, and noisy. The RPM will be limited to 2,000 RPM.
Your problem might be a loose connection, or a bad injector. It will have to go back to the shop that did the injectors. A injector balance test may locate the problem.
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.--- Jerry