if this truck has a throttle cable first check (pull on) the wires at the distributor and when you are absolutely certain that they are not broken rebuild the regulator. if it has no cable but instead has an eletric governor there should be a light flashing on the dash after the engine dies. i have seen this problem caused by a worn distributor gear causing chatter. the other thing to look for is a safety shut down system. this will be two relays and a timer and will look for oil pressure and over temp.
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