Here are the 02 sensor locations for the following codes on a 97 Blazer 4.3 vortec "W" in the VIN.

P0134 - Bank 1 / Sensor 1
Left side of the Y-pipe before the manifold
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P0154 - Bank 2 / Sensor 1
Right side of the Y-pipe before the manifold
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P0140 - Bank 1 / Sensor 2
Front of cat
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P0146 - Bank 1 / Sensor 3
Behind the cat
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But I still have the problem of the truck shutting down while i'm driving or just sittingwith the engine running - when i first ture on the key the radio will come on but the dash takes a second or two before any lights come on. the shutting down, could that by a result of the 02 sensor.