There are 3 common causes for this. 1 a failing crank shaft position sensor, 2 a failing cam shaft position sensor, and 3 a failing PCM (engine computer). Either one can act up when the engine warms up. Do this: try to get your van to an auto parts store like AutoZone and ask them to connect their scan tool to your vehicle and check for any trouble codes. If there is a code for "loss of crank sensor signal or cam shaft sensor signal" then have the appropriate sensor replaced. If there are no codes at all, then suspect a failing PCM and have it replaced. Most auto parts stores will connect their scan tool for no charge to you. Now if you do go with a cam or crank sensor, PLEASE use only Mopar brand sensors. I say this because I have seen some issues with the after market sensors installed in any Chrysler product.
Hope this information helps, and let me know if you need more assistance with this.
These symptoms happen even on a cold engine---does this change your advice?
Does it make any difference as to when the "scan" is done?? Immediately after the problem--or can it be day-week or anytime?