An OE windage tray should have the tabs opened up alot to allow the oil a big window to drain.
Try the extra quart, it could be that lil'extra you need and if possible, I know it's a bear to do, drop the oil pan and open up the trays drain back window tabs to at least horizontal and level.
If this dosen't help, it may be time to upgrade. Though 6000 - 6200 isn't screaming, drain back may be the issue somewhere, possibly the tray. That would be my first guess.