My oil gauge drops to zero, but everyhting appears to be working. could the oil pump be out? How can I tell?

Change the sensor. it appears to be a known issue.

https://www.autopartsrepairs.com/causes-low-drop-oil-pressure-dodge-ram-trucks/

Durango

https://dodgeforum.com/forum/1st-gen-durango/276936-oil-pressure-gauge-drops-and-rises.html

https://www.google.com/search?q=%2799+Dodge+Ram+1500+5.2L+Intermittent+sudden+drop+of+oil+pressure

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Hi assuming the oil filter has not become blocked, it sounds like the oil pump is not working properly. Of course it could be something more simple like a faulty gauge, sender or bad connection. But assuming again that the engine is suffering from oil starvation, I would get it checked quickly before you seize the engine completely. Good luck!

possible oil pump ,put a manual gauge on motor and test to see drop if it does its the oil pump but also check sending unit and gauge for fault

You are getting antifreeze in your oil. If you continue to run it the engine will be ruined. The oil pump will fail to pump foam. Sorry I can't tell you where the problem is. The first time I had this was with my 1953 Ford flathead v8. Luckily I happened to look at my oil pressure gauge just as it was dropping to zero. It needed a new head gasket.

It could be the oil pressure sending unit, or the engine could really have no oil pressure.
If the oil pressure dropped to zero at highway speed, I would expect the engine to lock up or at least make alot of noise.
You may have to tow it home and check the oil pressure with a mechanical gauge, or replace the sending unit to see if the gauge on the dash reads pressure.
The fuel pump gets power from the pump relay at startup, then runs off power from that oil sending unit when the engine is running.

you may have a faulty oil pressure sensor which needs replacing or a loose connection, check for any loose wires......hope this helps.....cheers.

Two things could be low on oil, or the pick up screen to the oil pump is starting to get clog, I have seen this a few time's on this type of truck here at my repair shop.

It could be a bad oil sending sensor, or the oil pump. When it drops, does the gauge stay on zero or fluctuates. The sending sensor isn't to bad to replace or cost wise, but pump is a different story. Have someone check the sending unit or just have it replaced to see if that's the problem.

It sounds like most likely its your Oil pump, if you have no pressure at stop and when you hit gas it sets the C/E light off, Guages in dash wont set off Check Engine Light. Replace Oil Pump.

Before you tear into the engine remove the oil pressure sender and install a hand held mechanical gauge and check the pressure. The sending unit coud be bad. As far as the rough running.. when was your last tune up?? The gauge could also drop to zero due to insufficient RPM's because of the rough running. Does it have any knocks when the pressure is at zero??