On my way up to the mountains this weekend, pulling my 17-foot toy hauler, I started getting a check engine light and the truck felt like it was losing power. Seems like it only lost power when I was going uphill and had my foot on the accelerator. had my buddy bring up his code reader, was getting a P0303 code third cylinder is misfiring. Had my wife bring up new plugs and a coil. Installed them while camping, thinking it was fixed, I headed home a few days later. Same issue happened, only under full load and going uphill. Any thoughts? My buddy mentioned drilling the inner cooler. is this still an issue on the 2016 F-150? Any help would be great.

 

Have you read this page:

https://www.obd-codes.com/p0303