The Dinan warranty you're thinking about runs concurrent with the original 4yr-50000 warranty, which you no longer have. otherwise they have a 2yr warranty on their parts.
the stutter you are referring to seems to be a problem with fuel flow and not your sparkplugs or gap. some run a step colder plug. not sure
i suggest you post threads like this in the appropriate sub-forum for better response
https://f30.bimmerpost.com/forums/fo...play.php?f=421