Sounds like by the time you got to the dealership the code had cleared and unless you do a lot of in town driving I don't believe your DPF was full. Not at 34,000 miles and this being the first time.

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2007.5 Dodge Ram 3500 HD,QC, 6.7L Cummins, 6speed Auto, 4X4, Bighorn Edition.
Click for installs: Carr Steps PML Diff Cover Edge Juice with Attitude Volant Intake Hankook ATM RF10