Engine swap

To do the swap could end up costing you too much money. Besides changing out the engine you would need a new wire harness and new computer. You would also need a new intake manifold and drive by wire throttle body. A new fuel rail with eight fuel injectors. New air cleaner assembly with a mass air flow sensor calibrated to the 5.3L engine. You will also have the issue with the engine mounts. It will be a different set up so you will need engine mount brackets as well where it may not fit the frame.

There may be other variables to this equation as well if the transmission control module will communicate properly with the engine control module since the modules communicate through the CAN Bus system. Software maybe needed to introduce the new engine control module to the system or for there transmission to operate properly with the V8 vs V6? Then you also have the cooling system which will be different. Water pump has the thermostat attached with the water pump. The A/C compressor and hoses need to be relocated. It can go on and on. You would be better off just purchasing a V8 truck then trying to do a conversion.

As JIS001 says you would need to change out pretty much every electrical item as they are all programmed to operate together. The PCM, wiring harness, BCM, instrument panel, ABS, even the radio all talk on the network and need to match the engine and transmission. Once completed you then may find that you cannot drive it on the road. That would depend on what types of state/province laws you fall under. In any places that do emissions or even simple plug in testing it would fail because you now have the wrong engine in it when compared to the VIN number.

Can it be done, sure. The best way would be to buy a 5.3 equipped truck, then you have all the parts to do the swap. If you decided to just buy all the parts piecemeal, you could likely buy a 2019 off the lot for less money.