I guess the question you are asking is if anyone else has a 2014 GMC 1500 that they use for a tow vehicle? I'm sure the answer is yes but why ask the question? I'm sure that the it would be similiar to the 2013 model in capability if not slightly better / more capable.
If you're wondering about weights and the ability of your new 2014 GMC 1/2 being capable enough to tow 6500lbs (GTW) then I'm going to go out on a limb here and say that you are mostly likley A-OK if you have the V8/tow package etc... that is unless you are also hauling a load of gravel in the back or something else to eat up all of your payload.
Best of luck to you.