[83GMCK2500]

I have personally seen a 6.0L in a 2005 2500HD work truck that was worked it's entire life and suffered a water pump failure and overheated at 370,000 miles. Cracked the block from cam to crank in a couple webs but those cylinders still had visible cross hatching with very little ridge at the top, couldn't catch with fingernail.

I bought a used 1999 6.0L to have rebuilt for my '83 and same thing...clean inside, very little wear cylinders, pistons, everything in great shape at 200,000 miles.

I don't know what an '05 Denali books for with 240k, but I think it's a great vehicle, definitely worth considering.