Its a 92, dodge dakota 5.9L magnum,

I notice that my gauge for oil pressure comes on for a while then dramatically dies after a little while. Its works when the vehicle is cold or just started, then after several minutes it drops on its face. I already swapped the sensor with one from the wreckers but the problem still occurs. Oil levels are good and there are no engine leaks. "I replaced the motor with a rebuilt engine, and its safe to say that it isn't mechanical.

I am confused on what seems to be the problem.

I also would like to mention, when I started the engine, I used a mechanical guage and I seemed to have oil pressure. 45 psi at idle, 60 under throttle.

 

Maybe swap the sensor with a new one instead of one from a junk yard.....

 

This.

They're known to fail.

Also, check the connector to the wiring; on my 1988, the oil pressure wire got pushed part way back up into the sensor, and it was driving me batty until I looked into the connector and saw it. Pushed it back from the wire end, and my truck picked up about 20lbs pressure immediately!

RwP