Oil pressure problems

[HotRodScottsdale]

I got a 1984 silerado, 350 small block bored 30 over forged crank with 68 Camaro heads and gear driven timing. All the work done before I got the truck, the previous owner ran royal purple 5w30 oil and I noticed the oil pressure gauge was all over the map. Idled around 20psi and jumped to max 40psi with any acceleration. I changed the oil and didn't see any metal and switched to royal purple 10w30 and it helped for a week and then it jumped all over again but truck ran and sounded amazing so I ignored it and kept driving the truck as a daily. Now yesterday day I noticed the gauge dropped to 10psi and only went up 1 or 2 psi with acceleration, I went to pull over and it snapped back to jumping again. Now today leaving work it dropped to 10 psi again and won't come back.

Where do I start looking? Oil on the dip stick looks good, motors not making any knocking or strange sounds, truck still runs great so I'm hoping it's a grounding issue or something with the pressure sensor.

Anyone have this issue?