Did you run a leak down test before you pulled it apart? That would tell you if it is a ring problem. They may look perfect but that does not mean that they are sealing. If there is lots of crank case preasure, the
oil may not drain back to the
oil pan going down the road. I had to run external drain backs off the valve covers to the side of the pan on mt 358ci motor.
Oil was stuck at the top of the motor. Is there evedence of oil in the intake passages going to the heads? Its possible that oil can be sucked out of the oil galley if the seal between the intake manifoldand the heads are not sealing properly. Good luck, scott