1999 Ford 150 after running for a couple of hours begins to miss. The condition lessens if speed is kept near 60-65 mph. The missing worsens (although intermittent) if speed is averaging 70+ mph.
Spark plugs are gap'd, there are no codes and the condition is very difficult to reproduce for the local shop to diagnose.

 

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1. You've posted in the 2015 - Present Ford F150 section. Post more appropriate in 1997 - 2003 Ford F150
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2. "1999 Ford 150" ... Need more information.
   HINT/TIP: Put your vehicle information (year, model, cab, trim, engine, wheelbase, _x4 drive, mileage, maintenance, modifications, etc.) in your signature -OR- provide it in your posting(s).
   
   *Telepathic or Carnac we're not.

.So you can imagine how difficult it could be not physically having the vehicle and pertinent information.
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