I had a shop replace the 5.3 with 215K miles, in my 07' Avalanche 4x4 LT, with a rebuilt 03' 6.0L, LQ4. (The 6.0 block casting#12551364), rebuilt 317 heads. All new ARP hardware and gaskets, new oil pump and water pump.
They re-used the 5.3 exhaust manifolds. Stock 6.0 cam and lifters. An upgraded newer style 100mm throttle Body, stock MAF, new ACDelco 36lbs. injectors, new ACDelco Iridium plugs and new wires. Two new Denso upstream O2 sensors. Reused the 5.3 coils. The original 5.3 was FLEX Fuel and had the active fuel management. The 6.0 does not.
Nothing was done with re-programming the ECM. My question is; should there have been re-programming to the ECM for the larger displacement? Currently I am using the truck as a daily driver. I would like to get the best mileage and performance from the up-grade, if re-tuning would be a benefit.