Speaking as a professional…
Speaking as a professional auto mechanic . . .
If the two cylinder sleeves are the only problem (and they probably are because each part is made on a different assembly line), if the job is done right, you will have no further problems with that engine, and it will perform for the next some hundreds of thousands of miles that it is supposed to. But to replace a cylinder sleeve, the engine has to be disassembled all the way down to the bare block. It just does not make sense to do that. And when you put it back together, it is no longer a brand new engine -- it is a rebuilt engine.
As a customer, I would only accept a brand new engine in a brand new truck. Not satisfying your customer is a big mistake. He is never going to buy a Chevrolet again, and neither are his friends and family members.
What the dealership should have done is swapped him out a different truck, and then repaired his truck and put it out on the line as a low-mileage one-owner used truck with a used truck warranty. The person buying the truck would be buying a used truck and could not have any complaints about the rebuilt engine.