Not going to comment on 454 grounds, someone else should know better. A really ghetto hack to investigate the issue is to put a jumper cable from battery negative to both the frame as well as the engine as extra grounds and see if anything improves (note that they don't like to stay put when driving about). Use at your own risk.
However to elaborate on the previous, the purpose of the lambda or O2 sensor is to provide the engine control module feedback about the combustion event, whether the fueling is rich or lean. Obviously, if the sensor gives faulty readings, the fueling will be adjusted the wrong way. Again this sensor is not used on a cold motor, or when you are at wide open throttle, because a normal O2 sensor is unable to get a reading in this condition (a wideband sensor is needed).
Looking at the Vortec 454, it may be that you even have three O2 sensors (left bank / right bank / downstream) so if there's a discrepancy between these it may cause a bunch of issues too. I am not sure how many there are because seems like there are variations. Then again, your problem could be something completely different.
However to elaborate on the previous, the purpose of the lambda or O2 sensor is to provide the engine control module feedback about the combustion event, whether the fueling is rich or lean. Obviously, if the sensor gives faulty readings, the fueling will be adjusted the wrong way. Again this sensor is not used on a cold motor, or when you are at wide open throttle, because a normal O2 sensor is unable to get a reading in this condition (a wideband sensor is needed).
Looking at the Vortec 454, it may be that you even have three O2 sensors (left bank / right bank / downstream) so if there's a discrepancy between these it may cause a bunch of issues too. I am not sure how many there are because seems like there are variations. Then again, your problem could be something completely different.