Okay, so, it's a 360, theres your first problem. Oiling issues abound. As they age, they tend to wear out, oil pressure tends to drop.
Now, lets assume its a healthy 360 and there isn't actually a major oiling problem, bad bearings or anything like that.
1. Are you using a mechanical gauge, or the gauge in the dash that at best is only a good guess?
2. What is "normal" and what is "10psi low" Please provide the numbers.
I wouldn't trust the factory in dash gauge, and a lot of folks don't. Mine is long non-op and I have always run a mechanical gauge that runs on a copper tube from the oil pump.
Here's what I would try, and in what order I would try it:
1. replace sending unit, cheap and easy.
2. Install, even if only temporary, a mechanical gauge. also cheap and easy, and you could rest knowing you have 2 monitoring systems if you left the sending unit in place.
3. is problem still persists, look into resurfacing the oil pump housing, or installing BJ's midplate assembly.
So, a little bit of info/story from my perspective, just for reference and to give you some numbers to compare to: When I bought my wag, the engine it had was putting out about 30psi at highway speed. That's bad. My idle oil pressure was somewhere under 10. Thats bad. The above was with 40 weight....which means its even more bad. I replaced my engine (with an engine that had about 155k on the odometer), and when warmed up on the highway, it's running about 50-55 psi. Thats good/normal. Idling, its still only 10ish. Thats not great, but it is what it is. That's with standard 10w30. Factory minimum spec for the 360 at idle is something silly like 13psi, or so I've been told.
I'm not sure if you read any of it, but recently i had a similar issue. out of nowhere i lost 10-20 psi. Idling was at/under 0psi. Highway was like 25psi. I was freaking out. Oh no, woe is me! I need another new engine! This ones gonna blow any second. I went out and bought new gauges hoping my old mechanical gauge was just on the fritz. turned out I found this... a chunk of RTV stuck in the inlet for the pressure gauge. I wiped it clean, reinstalled, and everything was right as rain.
I had a wrangler where the oil gauge would drop to 0 at stop lights. was sending unit.
My 2005 dodge magnum with the Hemi did the same thing, while i was on the highway and i about pooped my pants. Was sending unit.
So, what I'm getting at there is that commonly, if it seems like a sudden drop or change, it's probably something simple. Check what the others have suggested, and go from there. Should be easy peasy.