1996 Dodge Ram

Driving down the road the oil pressure drops off. So we put on a mechanical oil pressure gauge. When it is idling it seems fine but when you go to 2000 rpms it drops off again and then you let off the gas it goes back normal. There is a ticking under the driver side vavle cover. We just put new head gaskets on so we thought when we were cleaning the surfaces for the new gasket some dropped down and clogged the oil pump? Do you know whats wrong?