4l60e depends on how you treat it. In a light truck like that he should be fine as long as it's maintained. I'm at 192,xxx on my 2002 Yukon XL and trans is all original except for tailgate seal, fluid, and trans filter. Still running strong and shifting clean.
However I wouldn't attempt any mods at my mileage that would bump power by much without having another trans (4L80e) ready to go.