Engine oil pressure issue

[Papawolflopez]

Engine oil pressure gauge fluctuates along with lower rpm and a muffled backfire on passenger side between the speeds of 40-70 I have replaced the oil pressure switch the oil pump along with the oil pick up tube. Rearmain seal. Spark plugs

What could be the issue?

 

[Papawolflopez]

I took a video of what it does, but I don’t know how to add it

 

[Fless]

Host your video somewhere (like YouTube, etc.) and post a link to it here.