Own from birth 2006 GMC with utility body. All services and such performed by same mechanic. Called to inform him of oil pressure steadily declining to below 15 psi. Brought truck in, replaced obvious sending unit, drop transfer case to drop oil pan to check oil pump to eventually removing engine to discover spun cam shaft bearing in two locations. Is there no tolerance to saving the block? Besides scrap metal. Losing 900.00 for a core adds insult to the injury being that all maintenance was done. IS this the norm for the 6.0 liter engine?
Why are you being told to scrap the engine? Spun camshaft bearings are not common, but you replace the defective parts. In this case you would replace all the cam bearings, the camshaft, and the lifters because they wear to match the wear on the cam lobes. Push rods are reused. Since you're in there, examine the crankshaft and connecting rod bearings but keep in mind that in most engines, for oil to leak out easily past a spun cam bearing, it had to go through the main bearings to get there, so even though the oil pressure was low, those bearings were not starving for oil and will likely be okay yet.
I DO read quite a bit here about low oil pressure problems on a lot of different engines, but if there were some common problem with yours due to the design, why would you want to install another one like it? My vote is to fix what you have. Even if you do replace the whole engine for a relatively minor repair, there's no reason it can't be used for a core unless there's something broken or damaged beyond repair that we don't know about.