The other day I was wondering if there was a "high mileage" thread around here anywhere.
97 C3500 crew cab long bed 5.7 Vortec: 193,000 on the bottom end and runs ok after the repairs I've done.
I've owned it for ~10k and in that time have had the trans rebuilt. I started to replace the intake gaskets and ended up also replacing both cylinder heads due to small cracks, water pump and radiator while I was at it. And you can add to the list starter, alternator, AC compressor, front shocks, rear wheel bearing, in-tank fuel pump, brake light switch, turn signal switch and that like 1000 foot long brake line that runs to the rear axle (that rusted through right behind the gas tank - the only place you can't see it rusting through).
History is that the truck was owned by a metal building construction company since new, so driving to/from dusty/dirty construction sites, but also "fleet maintenance" - the service log I got went back over half it's life and about half of the entries were "4k oil change".