intermittent starting problem

I have a Trans Sport 94 3.8L. The van will run for about 20 min then either dies or if you turn it off it will not restart for a couple hours.
We Replaced the ignition module and it does the same thing. When it wont start there is no spark from the coil packs.
I know its not fuel.
Something electrical or sensor must be getting warm snd shutting off the signal to the Modulator I guess. But what could make it do this. Any ideas would be extremelly helpful.
The coil Packs seem to work fine. Doubt all of them are bad.
Bill

It seems it is a trend...look adjacent threads: most common culprit with these symptoms: crank position sensor, at that age, almost a mandatory maintenance item.
http://www.automotiveforums.com/vbulletin/showthread.php?t=760671