Mark Williams, of Pickuptrucks.com, takes a first look at the 2015 GMC Sierra 25003500 HD.\rbr\rbrOutside Phoenix, Arizona Zach Maskell got a feel for what these pickup trucks can do. There was a little bit of everything to tow from a front-end loader, to a large .\rbr\rbrMark Williams, of Pickuptrucks.com, takes a first look at the 2015 GMC Sierra 25003500 HD. Outside Phoenix, Arizona Zach Maskell got a feel for what these .\rbr\rbr2015 GMC Sierra HD 2500HD, 3500HD, and Denali HD officially revealed - engine is a Vortec 6.0 liter V8 making up to 360HP and 380TQ and a 6.6 liter .