Let's get your paranoid levels to a new high...lol. Possible crank thrust clearance too loose. A lifter galley plug behind cam gear not unstalled or improperly installed causing your oil pressure to dip low. Thrust flange grooved or worn even to let crank "walk". Cracked crank? Creating flex at certain RPM. Busted piston skirt? Wrist pin bore has a flaw and now "talking to you (especially at 2000 rpm). Flywheel/flexplate loose at hub or outer bolt holes. Have I got your heart rate up yet? Can you duplicate this condition while up on jack stands and using someone to help you run this thing to simulate? Try it and use a stethescope or what you have at your disposal. Use some brake action to simulate load too. It will change the attitude of this thing will trying to duplicate conditions.