If the 6 mile commute back in forth it the predominate use of the vehicle, especially if it involves a lot of stop and go driving, it is going to be problematic with any 2008 and later diesel because they use a DPF (diesel particulate filter). The DPF traps soot and must periodically clean itself by burning off soot and this requires around 30 miles of driving at 30 MPH or above to complete the cleaning cycle. It doesn't have to complete it in one drive but cleaning doesn't start until the filter is hot enough and if it is unable to complete in a reasonable amount of time you will get a message to continue driving at speed until it completes.
The Duramax engine has one of the better systems for this because it uses a separate injector to dump raw diesel in the exhaust stream rather than injecting it into the cylinders on the exhaust stroke like Ford which creates potential for cylinder wash down and oil dilution. But none of the systems work well when driving consists primarily of a number of short trips. You will also find mileage abysmal with any of the large diesel pickups in short trip stop and go driving due to both slow warm-up and the physics of frequently launching a near 8,000 pound vehicle. I am on my second Duramax equipped GMC and am about to order a 2018 but for shorter necessity trips I drive a Cadillac ATS and for short fun trips if it isn't too cold I drive a 2016 Z06 but its summer performance tires are not any fun below 40 degrees when they are like driving on ice. For your described driving if you need a pickup but can do without a HD model a 1/2 ton gas powered pickup will probably better suit your needs.