Check to be sure that your oil pump pickup is in the correct location or for some reason it might be loose where it enters the oil pump. It could have come loose and is sucking air instead of oil from the pan. The oil pickup tube could also have a hole in it somewhere. I had a 77 powerwagon that would loose oil pressure at anything above a 20 degree or so angle. Back on flat ground it would pickup the oil again. The pickup tube was loose and was not in the correct location I believe.