alway double check the guage your using,
i recently made this mistake on another vehicle and it cost me a lot of time and money.
My old gauge was reading low oil psi so i bought a new one, which gave me a low oil psi. I replace the oil pump and still had low preasure, turned out the new gauge of bad.

 

Thanks for all the input, I have changed the oil using 5W40 Rotella’s with a Mobil 301 filter, and the light was not working, so I fixed that, but still when sitting in “Drive” at a stop light it drops to as low as 5 PSI but the light doesn’t go on. If I push it into neutral it goes up to 14 to 17PSI. The Gauge is GlowShift and they sent me a new one but the results are the same. During the first 15 minutes of operation at 2K I have pressure between 46 to 51 PSI it is never steady. Can the oil pump just be weak or is it an all or nothing kind of thing

Thanks