stalls after warmed up

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van was given to me with a failed upper radiator hose . I replaced the hose , purged the cooling system. after about 15 minutes it starts running rough , like starving for fuel.put guage in line pressure at specs with and without regulator vacuum line hooked up. no codes set .tried swapping coil pack no difference.loosened the exhaust (thought the converter might be clogged).when cooled down it starts and runs normal.