Runs for a while and dies

I don't know if this is part of the problem, but I had a mechanic to fix my distributor b/c, my truck would not start. If I drive the truck for about 4 miles it drives fine, until I notice the oil pressure dropping slowly, then the truck cuts off. I wait about a minute then the truck starts up with oil pressure normal. When I drive a few more miles the same thing happens again.