occasionally the engine starts to hesitate

I have a 2005 Ford Expedition and when I am driving about 50 to 55 mph, occasionally the truck starts to hesitate aggressively as if it is not getting the proper amount of fuel. However, once I press the accelerator, the vehicle accelerates smoothly. I have had the truck for about 5 years. This is basically the only problem I have had since I purchased it. It has about 158,000 miles on it but a majority of the miles are hwy miles.

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