I literally just went through this. My CEL would flash at highway speeds. I read somewhere that the crank sensor could be flaking out at higher rpm. I replaced the crank sensor this afternoon and just took it for a hard test drive on the highway. No More flashing CEL! I also read that you need to do a crank sensor relearn after replacing it but right now, truck is running great so I think I’ll leave it alone. Hope this helps you!