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Your intertia switch is located under your right side of your dash, right around your heater/ac box, on the firewall, or to the right of the firewall.
Your fuel pump relay is one of the relays near your right side fender, near the battery.
Have you checked fuel pressure once the van stalls?
you could have a starter problem, I would check your voltage at the starter when it is giving you the problem. There are 3 terminals on your starter. The small one is what gives the starter signal to engage. If, when the problem is occuring, you have battery voltage at the small terminal while holding the key to 'start', you will need a starter. If not, your problem is elsewhere. Report back with your findings.