why would car run a half hour then stall on 1991 Buick Skylark

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runs fine awhile then it just stalls have to let it set about 15 minutes then it will run fine for a few then stall again
(3) Answers
number #1 is correct, does the vehicle fire back up immeditly or do you have to let cool
My guess is a defective crankshaft sensor.
Im having same problem. Research is telling me its either crankshaft or head gasket. Let me know which one you do/did and if it worked