The current All Terrain package is available in three different tiers on the Sierra SLT: All Terrain, All Terrain SLT Premium and All Terrain X. In addition to equipment from the Z71 package (skid plates, suspension upgrades), the All Terrain package adds Rancho shocks, an Eaton locking rear differential and more aggressive tires. There are some additional features and appearance changes, too. The more aggressive All Terrain X adds things like a cat-back exhaust and Goodyear Wrangler DuraTrac tires.
The truck in these spy shots is definitely wearing different wheels and tires than the Sierras we've previously seen. It also looks like it's sitting a little higher, just like the Silverado Trail Boss. This also looks to be an SLT model as it doesn't have the MultiPro tailgate. Expect the 5.3-liter and 6.2-liter V8s to return, but don't rule out a diesel-powered Sierra All Terrain sometime down the line.