No need for a 8.1 if an old 350 does the trick now. 6.0 will out pull it all day.
Yes very bulletproof IMO. Didn't have a lot of experience with them until recently but we have a bunch of old 3-4 tons construction trucks with them and the engines are about the only thing that don't need work.
Never actually owned a LS motor until a few weeks ago, bought a 2001 Tahoe 5.3. Great, simple, quiet, well laid out, relatively powerful engine.
I'm not a fan of newer 6.0s for their power compared to Ford 6.2 or 6.4 Hemis but they work. All day every day.