Oil pressure problem (or gauge problem)

My -89 B250 (318 v8) has a strange problem. It started yesterday. At idle the oilpressure reads normal or sometimes a bit higher than it used to. When driving (rpm going up) the oilpressure drops very low but not so low that the warninglight comes on. After I noticed this yesterday I changed oil and oilfilter but the problem is still there.
Is it the oilpump or is the gauge or the sending unit for the gauge?
Anyone has an idea?

Funky; does the pressure stay up if you rev the engine while sitting still, or does it drop the same way? If it drops, I'd think it was the sending unit or indicator like you think.

If however it stays steady, then it might be the actual oil pickup in the sump. Try backing up suddently (parking lot or something) and see if the pressure holds steady. If it does, then the pickup may not be working right.

Pressure drops if car is standing still and I rev the enginge. I was also thinking about the pickup because when driving if I let go of the accelerator and let the car roll, engine idling, the pressure does NOT go up until I brake as if the oil in the sump needs to be moved in some way.
I have been keeping my eye on engine temperature as well when driving but it stays normal. If it was not enough oil circulating should not the engine temp go up, at least some.

I'd start with the guage and sensor, test the voltage in and out (I don't know the specs) and see if they're working right. I haven't heard of pressure going DOWN when the engine is revved.

Did you find out what was wrong with your oil pressure? I have a friend with a 250 Ram Van that's got low oil pressure when in gear and idling. It gets worse when the a/c is on idling around 650-700 rpm. I have recommended my friend put a real old fashioned gauge on it. Do any of you know where the oil presure sender is on this 1996 Ram Van 250? It has the 318 motor.

Thanks!