2016 GMC Sierra 1500 Double Cab is the newer version with some differences, such as the model year, starting price, horsepower, and fuel economy.. First of all, the 2013 GMC Sierra 1500 Extended Cab is priced $3,775 lower compared to the base MSRP of the 2016 GMC Sierra 1500 Double Cab, which is newer by three model years. And finally, a bigger engine usually means less mpg. But the 2016 Sierra 1500 Double Cab has a more powerful engine and it gets 3 more mpg than the 2013 Sierra 1500 Extended Cab. Among similarities are the body structure, ground shadow size, height, and maximum occupancy.