The tailgate badge will still be a good indicator, just like the "C" on the front fender means that it is probably a Cummins. Sure, someone could have removed it, or added one. I personally have NEVER seen anyone put the Cummins "C" on a gasser, but it could happen. If you find a 2011 that has a build date (on the drivers door) for 2010 it will probably be the SO. The later in 2011 the build the more likely it will be a HO. Of course, since some said you cant go by the badges because they could be changed. There is no way to know if the engine has been changed or not. Like I have posted before, the biggest difference between the two is software. IIRC the front vibration damper and the torque converter where the only hardware changes.