1996 Ford e-350 with 5.7 V8

I have a 1996 ford e-350 van with a 5.7L v8. It runs great at times but will also just start missing randomly! It does this while idling and while driving, doesnt seem to be during any specific range of rpm. I have changed fuel filter, checked fuel pressure, replaced rotor cap and button, spark plugs and wires, and the throttle position sensor, air filter also even though it wasnt that bad! It also does not show check engine light or give any diagnostic codes when hooked up to the scanner! What should I be checking next?