misfire or what

[scott hetchler]

i have 04 6.0 and once and awhile it will miss I get no codes and no smoke today sitting at a stop light I noticed the rpm's go down to about 400 or 500 the does this sometimes when it does it will last for the day but then other times i can go weeks with no miss fire I have the egr vavle unplugged and a egr cooler delete on the way i dont know where to start ro fix this any direction would be helpful. thanks

[Goose350]

What are you using to pull codes?