I've got a 90 C1500 with the 350 TBI with 300,000 miles on it. Regular maintainence on it and still runs strong. The drive train has never been cracked open, other than dropping the tranny pan to change the filter. As long as it hasn't been abused and has been maintained, they can last.
2000 BlaZeR2, 2" BDS body lift, 2" shackles, tbar tweak, 32X11.5 BFG AT/KOs, HPP3, too many bolts ons to list