My Sierra had 310k when I got rid of it. But it was a 6.0/4l80 2500... Smoked a little but still ran great. And it had a hard life of towing car haulers and campers...
I figure a well taken care of 5.3 should be fine till 300k... However at that point you start to question reliability with the family in it... Lots of things start to wear and break 200k+...