I have a 1991 oldsmobile 88 runs fine till it gets hot and dies.?

after it cools down it starts right up again. had it to the mechanic on the computer, couldn't find anything wrong. just sitting and runnng it hasn't died. the previous owner would drive about 20 miles then it would spit and sputter and died. i'm wondering if it could be air control on the breather is shutting it down, or a sensor on the transmission or coil packs are getting over heated.