Cannot locate engine coolant temp sensor

97 Chevy Astro, 2WD, Automatic transmission, 4.3L V6. Engine temperature gage started measuring cooler and cooler starting a few months ago. Now hardly goes above minimum level after engine is warmed up. Bought a new OEM engine coolant temperature sensor but cannot locate it on the engine. I have a Haynes manual for the 97 Astro and it has a perfect picture of the location for a Silverado (son's truck) but it is not there on the Astro. Have removed air filter case and hose to see front of engine and the inside cover to see rear of engine. Can anyone tell me where to find it on the 97 Astro? Thank you.

I seem to recall them being on the drivers side head, sticking out horzontally, below the vavle cover. But I haven't looked, and I hope I don't waste your time.

There are two sensors for the cooling system.
The Coolant sensor for the PCM is a 2 wire sensor located close to the thermostat housing.
The Engine Coolant Temperature Gauge Sensor is a single wire (green) sensor located on the left head by the spark plugs