I have a 2005 F150 for almost a year now. 85K runs good previous owner had the intake gaskets replaced and recent plug change “within 10K”.
I recently took the truck up long windy roads and it acted up both times.

The first time 2 weeks ago I was just slowly going up the mountain road and near the top it seemed to downshift a little funny and the engine had made a chatter sound. “Sounded like a rocker arm chatter you would hear on an old school adjustable rocker motor” I just accelerated a little seemed to clear itself up.

The following week going up the same mountain I heard the same sound and the truck seemed to be losing power going up the hill. There is not a good place to pull over so I just continued to ease up the hill and towards the top I was getting flashing check engine light w/ noticeable power loss. At the top of the hill the light went off and I continued to my destination a couple of miles away.

On the way home truck ran fine and I used my OBDII scanner when I got home and it reported NO CODES found?

I have since driven the truck a few times to/from work "8 miles no hills" since w/ no issues. I want to be proactive w/ the issues I experienced and am not sure of what to look into, any thoughts?

 

A flashing CEL indicate's a detected mis-fire condition...what brand plugs were installed ?? COP may be going bad... these 5.4's are real picky on parts... good luck

 

That's a cop going bad. If you're getting the flashing CEL you will be getting a code soon that will direct you to the bad coil. Try to take it up the same hill a few more times to get the code.