Here's something I found online:
2001 Ram 1500 w/5.2L...
Cruise along just fine, put your foot in it oil pressure waivers a bit, decelerate and shortly there after oil pressure drops to 0! Plenty of oil in engine, can't be pump, or I should be able to cruise with good pressure.. do oil & filter change. Same problem still there. Do another oil & filter change, this time running 5-min flush through engine first. fresh filter and oil... start up, no oil pressure at all! I dropped the pan and found immense amounts of sludge in bottom of pan. Figured the sludge is being sucked into sump screen under "increased pick up rate" ie: acceleration, and clogging the screen. Using the 5-min flush increased the amount of sludge in the pan from top end, including a lot of very hard chips of carbon, not nice. After cleaning pan and sump screen as best as possible, reassembled, fresh oil and filter, oil pressure was normal, engine performed well, for about 1500 miles, and then started doing the same thing. I started doing oil changes every 1500 to avoid this issue until the 46RE tranny gave out. Having to rebuild tranny now, I pulled engine figuring I would disassemble and clean the engine.
I could not believe the amount of had carbon and burned sludge in the top end of this 318! I also found signs of a head gasket issue indicating some blow by into the lifter valley at one cylinder. Cleaned engine, reassembled with new gaskets, did not replace oil pump as I had already replaced it not that many miles ago, and guess what.... oil pressure problem is still there!
Now dropping pan again, and replacing both pump and sump screen.
Note this crud gets nicely embedded in the stock sump screen, and # 2 any crud that gets through potentially can lodge in the over pressure bypass valve on the oil pump.. a good rev and that valve is by passing pressure back to the pan, one piece of crap in the valve and valve doesn't close... you get no oil pressure...
Seems like alot of people have this problem.