Oil pressure issue

Hello all! As the title suggest im having an oil pressure problem. I just changed valve cover gaskets do to a slight seep around the seal. Oil leak has now stopped but the next morning driving to work my pressure guage was reading 35 psi instead of its normal 40 and not climbing when I would accelerate. (It normally climbs to 60-80 psi). On top of not climbing to its normal level the pressure randomly dropped to zero a couple times and I immediately pulled over but the guage would go right back up to 35. I changed the sending unit but im still only sitting at 35 psi and seeing no fluctuation... Any thoughts? Im assuming I need to drop the pan and change or clean the pump and clean the tube and screen but was looking for any other thoughts before doing so. I also have a lifter or to rattling somewhere? Could I have just gotten gunk stuck in under a lifter? Would this effect pressure? Thanks for any help.

I'd change the pump and clean the pickup. The pumps are pretty cheap compared to a new engine. It's very possible that removing the valve covers let some crud down into the engine and its been sucked into the pump/filter screen.