What makes you think they are dying? Have you pulled any DTC codes from the ECU? Where is the sensor situated in the pipe. Bottom, 1/4, 1/2 way point, 3/4 or top? The best spot for a sensor that runs in a pipe parallel to the ground is 3/4 point or top of the pipe. This helps to keep the sensor dry from condesation when the engine is off and helps to avoid premature failure. A minimum would be on the side (half way point of the pipe). Are you using any fuel additives? Is the sensor circuit open or shorted (harness issue)?
Have you monitored the new sensors for proper voltage fluctuation with the Nismotronic software? Have you datalogged the o2 sensor?