Heard the same from folks around here - the 6.4 & 6.7 don't like stop 'n' go driving. Better off work'n them hard all the time - they seem to do better when they're run that way. That's what worries us - our app (farming) works'em pretty hard but includes quite a bit more idle - low speed ops than most. Granted they're loaded but we might only be going 10mph. Worried we wouldn't regen enough and have issues.