Everybody I know who owned a V10 said it was a POS.
The 6.0 is good if it's bulletproofed, as described above. I've always wondered, though, about how great an engine is if all of these things need to be done to make it durable?
A 7.3 Excursion is a unicorn. Very hard to find, and very expensive if you do find one. Yes, it's basically a medium-duty truck engine, but it's so damn heavy that it actually reduces your rated payload and towing capacity by a not small amount.
Yes, as James mentioned, I've towed some beasts into the Rockies, including Powder River Pass (9666') and the Eisenhower Tunnel (11,100'). You won't be winning races, but you won't be a menace either because you'll still be able to go faster than the big rigs. The 6.0 loves to rev, so let it eat.
This is approaching the Eisenhower Tunnel with a GVW of just over 16,000 lbs..
My current rig, parked at Wall Drug: