Your PSI at a cold idle is irrelevant and isn't going to help with a diagnosis, so just keep that in mind. Also, all oil pressure goes up when moving parts start moving more, so that probably won't help either.
The point at which you need to troubleshoot is at a warm (210-degree) idle. Your oil pressure at that temperature, at an idle, is all that really matters.
You saying that you have no knock is a good thing. So I would start with a mechanical gauge. With this, you can verify whether or not the factory gauge reading is correct or not. Very often, the pressure sending units go bad on these Cherokees, and a mechanical gauge will tell you if it did or not. If you don't have a mechanical gauge, then just go to Advance Auto Parts and get a new oil pressure sending unit and put it on and see if it solves your problem.
If your pressure sending unit isn't bad, you can always try using a different oil or a high volume oil pump. These won't cure oil pressure problems, but they can help hang you over where you need to be temporarily until you have a mechanic check out all of your main, rod, and camshaft bearings for wear.