If you take off the wire to the oil sending guage and hold it onto a ground point the guage should go peg to full high pressure if it doesnt its usally the guage, if it pegs out its usally the sending unit,
One time my ford truck (79 F250 400 cid) did that after 100 or so miles after a oil change, had no oil pressure over an idle, I changed the new motorcraft FL1-A oil filter and it worked somehow the filter was clogged or was a manufacter defect | 
