And one of the test they do to see if the DPF is bad is Rev the motor and see if black smoke comes out the tailpipe. I'm trying to find where I saw this at and I'll post it up.

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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