Engine swap?

They are entirely different engines. You would basically need to swap all of the modules and harness from the Caddy into the truck. No way to flash the ECU like that as they are different. BCM is different and much more. Not something that is really possible to do.

LS swaps are done by the hundreds these days, so I know you can reflash the ECU and use in another vehicle. What do you mean by "all the modules"? Are you saying because ones GMC and ones Cadillac the PCM, BCM, and TCM won't communicate? Could I do a standalone ECU? Is there a way possible that is cheaper than buying an engine or new car? I still owe a lot on the Acadia (only had it a year), and I can't really afford another vehicle.

Yes LS swaps are common, but that isn't what you are doing. The only items your vehicles have in common is that they were sold by GM. None of the rest interchanges. The engines mount differently, the transaxles are spaced differently, and you would need to swap the transmissions at the same time because they are not the same internally. Now you need to make the mounts and the exhaust. Then you need to swap the wiring and ECUs as well as the BCM because they are VIN locked and cannot be interchanged. The BCM is also VIN locked. Basically, you would need a completely custom tune for an unpopular engine platform for swaps.
They are based on entirely different platforms as well so none of the mounts and such interchange either. You would be fabricating most of those parts. It's not really a feasible thing for a low budget build. I would say you would be looking at closer to $10,000 just to get the engine into the truck, then add another $5,000 for the electronics. You can get a replacement 3.6 for far less money.

I'm not sure you know what I'm talking about. Bot vehicles are AWD crossovers with transverse mounted engines. And both engines are gm high feature engines. I have read somewhere but can't find any real proof that they are the same block but there are sleeves in the 2.8 limiting its displacement. Why would internals of transmission matter?

I know what you are talking about. I also know that they will not swap the way you think they will because of the design and mechanical differences in the two vehicles. The engines are also of two different generations, they have multiple internal differences and wiring harness connections. As such you need the correct harness, which in turn needs it's own controls. As I said earlier, yes it could be done, but not at a low cost and not as anything approaching a bolt in.

Okay, thank you.

You are welcome. Sorry it seems like I'm against it, I like doing swaps and improvements but am also realistic about the pitfalls and foibles involved, especially in modern vehicles, and it is unfortunately getting worse with each new design.

Yes I agree it's getting almost impossible. I've done more research and found out the newer LFX engine is cheaper and will work with only minor adjustments so I'm going to look for one of those.