Oil pressure

2000 dodge durango 4.7 liter after driving for about 15 minutes the oil pressure gauge went from 40 psi to zero then went back to 40 after 10 to 15 seconds oil level is at proper level removed the oil pressure sensor and installed on oil pressure gauge (manuel gauge) when i started the engine the oil pressure was reading 40 psi after it ran for 30 minutes the pressure was 30 psi ran the engine to 3000 rpms pressure was 60 psi took it down the road about 15 miles oil pressure started to drop went to zero then back to 30 let it idle watched the gauge it was at 15 psi and with in 5 minutes it dropped to zero is the problem the oil pump or could something else cause that and if it is the oil pump how much work is it

Just for fun, try a new filter first. It’s only $5 and may solve the problem. Other than that, it does sound like it could be the oil pump, or the oil pump drive, depending on what the pump is driven off of on this engine. Also, possibly something could be clogging the oil pickup in the pan. Replacement labor will depend on where the pump is located and how easy it is to pull the oil pan on this engine. A Haynes or Chilton manual may have information on this, or you could call around to shops and see what’s involved. I’ve never worked on one of these so I can’t give you more specific info. Good luck.