Think it was an option they added mid model year?
Did go to GM's site just to see if anything had changed for the Z71 designation with Tahoe/Suburban. The only thing that impressed me was that they mentioned you had to get the 4wd.
Synonymous with off-road performance, the Z71 package adds a front skid plate, off-road tires mounted on 18-inch wheels, a unique grille, running boards and “Z71” identification inside and out. Fog lamps, front tow hooks and front parking assist are also included.
“The popular Z71 package enhances the capable look and feel of the new 2015 Tahoe and Suburban,” said Sandor Piszar, director of Chevrolet Marketing. “It gives customers another choice when it comes to selecting the full-size Chevrolet SUV that’s perfect for their lifestyle.”
The Z71 package is available on 2015 Tahoe and Suburban LT models with 4WD, with vehicles produced starting in October. Those vehicles also benefit from additional content added midway through the launch year, including OnStar 4G LTE with a built-in Wi-Fi hotspot, wireless phone charging capability and hands-free liftgate operation. http://media.chevrolet.com/media/us/en/chevrolet/vehicles/tahoe/2015.detail.html/content/Pages/news/us/en/2014/Sep/0925-tahoe-suburban-z71.html