We had the same thing happen in a 98 dodge caravan. Went through mosto f the same things you've done. What it came down to was the computer was loosing communication somewhere within the wiring harness. They pretty much completely gutted the van and replaced the whole harness. Started right up and never had a problem sense. The tech wracked his brain for about 4 or 5 days before he decided all that it could be was the harness.