I just spoke to my dealer about a 5.3L remanufactured crate engine. I figured they'd be a good starting point. The price of the engine wasn't astronomical BUT labor to swap in the new one was. For $3,000 I'd consider doing it myself instead and swapping an engine is pretty intimidating to me.
I found out some interesting things when I was talking to both the service and parts departments:
-The new reman engine has a 3 year/100,000 mile warranty. That seems pretty good to me.
-I asked about if GM has addressed the cracking head issue. They told me according to TSBs and superseded part numbers of the heads, the heads have been revised to prevent cracking. Who knows if they're able to fix the production heads or if you have to buy brand new heads though. They said the crate engines all have the latest heads though. Although I don't know if that applies to reman crate engines? I don't know exactly how that works.
-As best as the parts department could tell, both flex and non-flex versions of the 5.3L engine share the same part number. That makes sense to me because as far as I know everything that's different about the flex fuel versions is outside the engine like fuel injectors/rails and a flex fuel sensor.