'17 Expedition, 3.5L Ecoboost misfiring(?)
 

Not sure if it's actually a misfire but I'm not sure what else to call it. Happens most often when I'm in 6th gear and need to accelerate to either pass a person or maintain speed going up a hill. It is best described as a stutter. You can fell it miss, the car stutters and jerks, no "get up and go". If I continue to push the pedal, the check engine light will begin to flash at me. Once I back off the throttle and just keep a steady pressure on the pedal, the egine will eventually even out and the light will quit flashing. Unfortunately, it won't store any codes so I have no idea where to start trouble shooting.
I've replaced an O2 sensor and the spark plugs but neither of those resolved it.

2017 Expedition Platinum, 3.5L Ecoboost, 142k miles.

There could be several causes for a misfire. Usually ,, a misfire under load can be attributed to a coil or coils breaking down under load.