Small Block & Big Block Chevy Specific - pil pressure acting crazy 5.7 vortec

I have a 97 gmc seirra with the 5.7 I was driving my truck around today and noticed that the oil pressure gauge was jumping around a lot then on my way home the needle dropped below the 20 psi mark and the check gauge light came on at an idle as soon as I press the gas oil pressure climbs. It was a quart low so I filled it but that didn't seem to make a a difference. I let it cool down and starte it and let it idle up to operating temp the oil pressure is still jumping around a lot between 20 and 40 psi. I did replace the sensor a few months ago. Any ideas?

New sensor gone bad. Have you hooked up a mechanical gauge?

No I was planning on doing that but have been busy the last few days

Yea, I would put a good mechanical gauge on it and see what's happening. I have seen a lot of aftermarket sending units go bad quickly. Don't buy a cheap aftermarket gauge, get a good autometer. You will probably have to get a t under the stock sender as most fuel pumps run on oil pressure.

I did recently have a head gasket blow on it. Could the water being mixed in with the oil have messed up the sensor

Possible, but I can't confirm it. Water is hard on bearings, but the pressure would usually stay steady not jump around. It would stay low after it warms up.