What would cause engine to die while reving in both neutral and park?

Well there has been 3 times when my engine dies when i put it into either neutral or park and try to rev the engine… Im not even revving that much, it dies on very mild revving.

What are some things that would cause this to happen, just list anything that would cause this? Its a 1990 GMC Sierra (C1500) with a 5.7L chevy small block if that helps any