I was checking out an '09 Chevy and the saleswoman told me that once a month OnStar runs a diagnostic check and send you the results. My first thought was I wonder if they'd notice that I tuned the truck with a programmer and removed the DPF. If I was going to buy a new GM, I'd be getting rid of that DPF at the earliest opportunity. I wonder if OnStar would catch it and what kind of problems it would cause.