The great thing about the 6.0 I had is it changed its own oil.
You just kept adding it and it leaked it out on its own.
And that was a NEW truck.
This isn't a Ford/Chevy/Dodge thing to me. Ford made Granadas... and they make Shelby Mustangs. The 6.0 is just the worst offering from a company that does make other very excellent engines.
I prefer the Cummins because it's an inline 6 and a LOT easier to work on, because I do all my own work. I like Fords. I'd steer the OP to either a newer Ford or an older one with a 7.3, or else a Cummins or Duramax. If it's a Duramax, go for an '05 or '06 "LBZ" but not an earlier one than that, the earlier ones have cylinder head issues. I'd love to have an '06 Duramax with the Allison auto trans, that's the hot setup if you like just old enough to be affordable Chevys.
Definitely don't just go buy whatever pretty diesel pickup the dealer has on the lot without doing a lot of research on that particular year and model. The Big Three all made great trucks I'd be happy to own, and they all three have particular ones to be avoided.