Makin' Do

I just replaced the opti in the 95Z that I bought and it runs 100 times better. Starts great every time and idles fine. The problem I am having now is when I drive it long enought to get it up to operating temp (not my daily driver) sometimes it will start loosing power. It will kind of pulse. Three times it has died on me as I was driving down the road. I just coast off to the side of the road and wait about 30 seconds, then it starts right back up and keeps rocking.
I read the codes and the only thing it is giving me is 15='Coolant Temperature (ECT) Sensor Circuit (signal voltage high, low temperature indicated).' Could this be the problem. It doesn't show hot when I am driving. In fact, id hasn't got over half of the guage. Any Ideas would be much appreciated.

thanks
Matt

my1994z28

There are 2 sensors,one is in the water pump,that the PCM reads and the other sensor is in the driver side cylinder head,which is temp gauge.Change the sensor in the water pump.