Ford: Ford

Question
QUESTION: I have a 1990 Ford F 250 with a 4.9 inline 6 the truck idles great but after the truck reaches running temperature it starts to bog down under high RPMs what could cause this problem

ANSWER: Hello, has any recent work been done ? Ie... Maintenance ? Does the service engine light come on ? Are you driving it when it does this or just idling and you are raising the isle manually ?

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QUESTION: The head on the engine was replaced.the service light is not on. It only does it when driving. When parked it runs fine during high or low idle

Answer
So at a steady cruise high speeds or any speed, it surges or starts losing power ? Are you familiar with the engine components ? Try disconnecting the EGR valve by taking the vacuum line off it and reroad test . If that doesn't take care of it, locate the fuel rail and disconnect the vacuum line from the fuel pressure regulator and reroad  test and get back to me please