oil pressure,lost all oil pressure, replaced the oil pump, low oil sensor, oil pressure sensor, oil pan gasket,

2001 GMC Seirra 5.3L V8 Vortec, lost all oil pressure, replaced the oil pump, low oil sensor, oil pressure sensor, oil pan gasket, timebelt cover gasket therostat/housing, truck cranks but still no oil pressure..if u rev motor and keep it above 2500 rpms, there will be around 15lbs of oil pressure, take foot of gas pressure drops to 0 and truck dies…what am I missing???

My car has 210000 miles.
My car has an automatic transmission.