I have a 429 and experiencing the same issues under load. At a stop with no motion I can rev. it up all day long and the
oil pressure increases with the RPM. Once steady driving like on the highway no problem either. When I accelerate or go into a corner the
oil pressure will drop from about 50 PSI to about 20 PSI. I have put my problem down to the fact that I have a modified front sump
oil pan. When I built the engine I shorten the sump by 2" and lengthen the sump to maintain volume and put in a baffle gate to stop oil flow from the pickup. I don't think it worked. When I get on it a little or go around a corner I think the oil slops away from the pickup or gets foamy which may be the cause of the drop in pressure. I am hoping by putting in a rear sump pan (Canton Road Race) it will correct the problem. I am getting nervous when I read this thread, time will tell.