The report the garage gave me says: Check Engine Light On, DTCs P0171, P0300, P1174 Set - perform injector test, replace injectors & reprogram ECM. Correction: This condition cannot be corrected by cleaning the injectors. (I ran injector cleaner thru 2 tanks before taking to garage & the garage also did an injector cleaning the first time I took it in but after 2 days light was back on. I finished running the tank out but after refill light was still on & that's when the garage said to bring back for further diagnostics.) Perform an injector balance test using the Active Fuel Injector Tester, CH-47976 procedure in SI. If any injector is identified as having a lean condition, replace all 4 injectors with the revised injectors. After installling the new injectors, reprogram the ECM with updated calibration files using the TIS2WEB SPS application. There are 2 calibration part numbers that are valid for "Engine Operation". Select the part number with the description that reads for vehicles with 2nd design injector. The injector has a dark blue overmold color for this repair. IMPORTANT: The fuel injecors must be replaced & the new calibration files must be installed to ensure a complete repair. Failure to perform both repairs will result in the same condition. Parts: Part #12602480 Fuel Injector - 4

I would ask the GMC dealership if this is covered under an extended warranty. Check to see if this is something that might be a recall. Sounds like a manufacturers flaw, some Ford injectors have extended warranties.

Please tell us that they actually looked over stuff like the injector harness and the condition of the air intake tube and the MAF sensor... a cracked intake tube or dirty MAF could cause a lean code and it snowball into the other symptoms...

I don’t know why the PCM would *have to* be recalibrated for an injector swap, if going to same size and style and impedance it shouldn’t matter... however a not insignificant number of 2006 L61 an LE5 engines were known to have faulty injectors (they crack and leak causing your lean condition (P0171) and misfire(P0300)... I can’t remember if it was a full out recall or just a TSB but either way you could talk to your dealer about an injector recall...

as as an alternative to paying dealer rates, you could purchase a set of “performance” injectors from a tuning company like ZZPerformance, and have them tune your PCM for them... don’t know if that would be cheaper than a dealer fix(non warranty) but