Piston slap affected more than just the 6.0. Some have it, some don't. It is more of an annoyance than a longevity issue. My 2001 6.0 had no signs of it at 135k when I sold it, my mother's 2002 5.3 Tahoe does, her 2002 5.3 Avalanche does not, my brother's 2003 6.0 with 300k miles did, so did his 2001 6.0 with about 80k when he sold it. Just listen to it, if it sounds bad enough that it will bother you, avoid it. Listen to it both cold and warmed up.
The only real 6.0s to avoid, and this is more for an engine swap aspect than in the truck is the 99-00 6.0s because they were iron head, and had a 0.400" longer crank, which won't mate up to the other later model GM transmissions, although it is just fine with the 4l80e, NV4500, and older transmissions like the TH350, TH400, 700R4, etc. (The 01+ 6.0s used a 0.400" spacer to mate to the 4l80e and a 0.400" thicker flywheel for the NV4500)