96 Voyager Stalls Randomly

Last night after traveling for about 50mi my 96 Voyager LE 3.3 quit at about 65mi. After pulling over it started immediately and quit 5 sec later. Then nothing, the starter would not engage (outherwise there was plenty of battery power--lights, radio, etc.) after trying intermittently for about 20 min it suddenly engaged and started getting me ten miles further and home. The same thing happened again today but after only about 1/3 of a mi and much less time for a restart. This is a problem that has been occurring about twice times a year since the van had about 20,000mi (now above 100k) and it runs fine in-between. There doesn't appear to be a pattern--speed, hot cold weather, lenght of travel, etc.)--the dealer was never able to fine a problem-the codes were gone by the time the van got to them. Any thoughts would be appreciated.