2004 chevy 2500HD LLY Engine Miss at 65 mph when warm, no trouble code during miss. The only code has been 401, 404 dealer replaced EGR and I still have the miss and the 401, 404 code. I suspected injector trouble but dealer thinks now it may be the MAF or Map sensor. What are your thoughts?

I just got done with mine havein a miss and i changed injectors and fuel rails and it went away. mine wasnt really isolated at a certain speed but it was a lot worse at higher speeds.