transmission problem? on 2006 Ford Expedition

My 2006 expedition, 60K miles, hesitates or falters when I ease off the gas (even slightly) at highway speeds. The problem is intermittent but gets much worse after I have been driving over an hour. The vehicle is fairly well maintained; regular oil changes and fluid levels checked. Any ideas?

1 answer
Start with checking for diagnostic trouble codes in the PCM. If the spark plugs have never been changed, I would recommend replacing them. Check for vacuum leaks.