Being as everything else on the suburban is original im assuming the o2 sensor was too so i replaced it. but it still runs a little rough but doesnt cut out near as much. Ive noticed now that it runs better when its cold than after its warmed up.
The ECM doesn't even look at the O2 sensor until it goes into closed loop so replacing the O2 sensor would not make it better when it's cold. Clear your codes and see what comes back. Go back to basics,
Tune up, make sure EGR is closed at idle, good fuel pressure, then see how it behaves. If it's still acting up you'll need to do some pinpoint tests.
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