I have a 2015 XLT and experienced the same issue when I was towing my travel trailer through some hills in central Utah. The code turned out to be a P0303 which was for a misfire. I was able to stop a few times and the light went off, but then would come back on when I was really pushing the engine to get up a hill. I was able to find a shop and we replaced all the plugs and the coil pack for #3. That resolved the issue. The guy changing the plugs said #3 actually felt loose. I only had about 20k miles on that set. The shop used NGK 97177 plugs which I see are gapped at 0.032
One related question about driving while the Check Engine Light is flashing. I've seen other posts that mention that is dumping fuel and will kill the Catalytic Convertor. Anyone have any idea how long would that take to actually kill it? Also, if I drove it long enough in that state is the Cat degraded in that it is impacting my current performance? Anyway to test it?