I would probably take the gasser before the diesel in this case. 6.0 Vortec is actually a good engine, but GM transmissions have left something to be desired in the past 15 to 20 years. The Duramax diesel has a reputation for fuel system problems.
"Cheese Wagon" <firstname.lastname@example.org>
Former owner - 1989 Ford B700 64-pass Blue Bird (Rest In Peace, Cheese Wagon)