Oiling problems

Try the extra quart as a diagnostic tool. It sounds like your either running out of oil of having lifter pump-up or down. You may need to also check to be sure your cam is up to the rpm you are turning and also the lifters and springs. I once was floating the lifters at 5200. Changed to what is use to be called anti-pump up lifts and went to 6500 with no float.
Rumble is dead right about the windage tray. If you don't get the oil drained fast enough it is slung back into the block, robbing HP and causing oil foaming that could endanger your lubrication of the bearings.