Need help quick please oil problem with new motor

[302crew]

okay i just got my new 306 dss block i bought it off a friend he hasnt ussed it in about a year i put it in it runs fine smooth but i looked at my auto meter oil gauge and i have 0 psi at an idle and like 20 when its reved up now i have the clear oil line going to the gauge the oil never even makes it in there then when i rev it it goes in a little and and if i let off the gas it all flows back into the motor the one think i was thinking it could be was when i put the motor together the gaskets between the pick up and oil pump and oil pump and block werent in to good of shape could this be my problem i know it has some oil pressure cause i know what a motor without sounds like any advice would be greatly apriciated thanks in advance