Oil pressure gauge needle "flutters" wildly after engine is warmed up.

What is your question?

Pressure holds steady at start up but within minutes begins to bounce/flutter wildly from side to side during idle and at 75 mph. If I press the accelerator and raise the rpms up by 5-10 while idling, it maintains steady at around 40 lbs. She has done this since I bought her 4 yours ago and I keep a vigilant eye on the entire oil system and only use Castrol 10W40. Actually, almost every needle in my dash flutters/bounces. I am never sure whether I am going 60 mph or 83 mph!! Thank you for the way you answer questions, I hate being talked down to.