3406e Cat cold missfire

I just bought a 98 Pete with a 3406E cat that has a misfire when it is cold after things get nice and hot it goes away. the guy I bought if from told me it would be that way because the cat dealer said the ecm needs to "relearn and it takes 64 run cycles to do this" I am very skeptical of this. Am I wrong? My thinking from what I have read is either bad injectors or injector O-rings. I have no idea what the serial number is because the tag is missing and I can't find it stamped anywhere yet. Any help would be greatly appreciated thanks in advance.

 

Thanks for the reply I will try to get some one to check the ECM or swap injectors around.

 

Head gasket was my thought after doing so research. Guess I will just have to change it. Thanks for the replies!

 

I know it has been a long time but I just got the truck in my shop to check it out. (work two full time jobs so time is limited) Well found all lower orings on injectors bad as well as middle one on number 6 was gone. Going to have all injectors bench tested and install with all new orings. While I have it apart I am considering changing out all injector cups and orings. Engine is suppose to only have 300k to 400k on it but will do all this anyway.