Pull the distributor and check the gear. You might find that the gear is not correct for the roller cam and is destroyed.
Vortecs require "melonized" or pickled gears. The steel gears fit, but don't last. As they wear, timing gets out and they miss when idling and under heavy load. This can be observed in ign timing dancing around prior to failure.
A grossly failed distributor would cause what you describe. Distributor drives the oil pump. And, a failed oil pump will destroy the distributor....and every thing else. Dist failure is common enough, oil pump failure is rare. If the engine still turns, might be salvageable.
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