GM tested these engines to 300,000 miles, 3 reasons newer engines last what they do:
- better oil ( ok not for flat tappet camshafts)
- no choke
- coil near plug ignition
The last 2 means that the engine needs way less enrichment/duration during cold starts so less oil wash down.
For sure an early (say 2002) 4200 might need to be gone through but the cost of the engine is going to be a lot less also.
Later engines bolt them in.
My 2006 Colorado has 140,000 miles on it and running strong.
