I would still pay attention to this image, not due to its accuracy, but as an indication of direction the styling and design may be taking. It may not be spot on, but mesh in the NNBS and you'll see what is more likely to come out. I doubt the C pillar will be that thick, but the angle might be close to actuality. Very likely no vents in exterior of door. It serves no purpose. Brake lights won't run all the way up the D pillar. Make it a little more broad in the shoulders and carry the fender line all the back for the bottom of the windows. I anticipate more chrome accents for the front grille, windows, door handles, etc. If you want a real taste of exterior styling just look at everything GM is coming out with. Yukon could end up with a more pronounced and squared grille (2013 Acadia and current Terrain), stylish bends and ceases that server no functional purpose (2014 Impala), squared tail lights with rounded corners (2013 Malibu). This new truck is going to scream tough and stylish. Don't be surprised of the Tahoe grille gets angled on the sides and runs down past the headlights.
What most people don't notice about GM design is that only minor tweaks are made for a revision of a vehicle that keeps the same name from one generation to the next. We don't need to look any further than the history of the Malibu, Corvette, Impala, Silverado, Tahoe, Suburban, etc. to see this. When GM changes a cars name it also goes through a major redesign. Case in point, look at the Cavalier to Cobalt and Cobalt to Cruze change overs. Aveo to Sonic, S10 to Colorado, Blazer to Trailblazer, and Trailblazer to Traverse are excellent evidence to this argument.
As for the powertrain, I've heard the transmission is likely to remain the 6L70e, or be revised with an additional gear, making it a 7-speed. The 5.3 is likely to bow out with a revised version that increases displacement to 5.5 via direct injection. Everything GM is making is getting this treatment. It improves horsepower and fuel economy. Numbers I've heard being passed around are 370-400 for the trucks and up to 440 for the Corvette. Estimated highway mpg its aimed for 30, but likely to fall around 25mpg for the trucks. 30 is more likely in the base model Corvette.