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5.4 f150

My 5.4 ford engine with 6 speed transmission does not run smooth between 35 an 40 mph. The rpms fluctuate. Is this normal?

Is that a speed at which you often cruise. If so the throttle position sensor would be my first guess. Have you had the computer scanned?

I have noticed the fluctations afetr coming down a hill and taking my foot off of the gas. I have not had computer scanned yet. Thanks for you reply.