Welcome aboard. Sorry to hear of your troubles - especially with a brand new truck! I own a C4500 Kodiak - unfortunately, the number of medium duty owners here on TheDieselPage.com currently is low. I don't recall seeing any posts from other 7.8L owners. However, some of the problems you may be encountering could be common across the Duramax family, the new DPF systems, or diesels in general.

Usually, 'bucking' is fuel related. Something is interrupting fuel flow or varying fuel pressures. Being it is winter - could you be experiencing gelling problems? What fuel are you running? Have you tried changing the fuel filter(s) and running a winter blend fuel or #1 diesel?

Fill out your profile and signature line with location and truck info - it will help us to troubleshoot - i.e. if you live in Cali, please disregard the gelling suggestion...

(Moderator, please move this thread to the Duramax forum - we'll move it later to the Medium Duty forum.)