Jalopnik.com has posted some pics that just may be of the vehicle mode of Ironhide. If not, its still a very sleek custom job that I wouldn't mind on my car.
"...it is a GMC Top Kick C4500 4WD Crew Cab (not a K4500 anymore, now they're C4500 4WD, so confusing!) with a Monroe upfitters' bed and from what we can see a whole lot of custom work too. The badass tires that Seth L commented about are the Nitto Mud Grappler...Fun fact, the bed on Ironhide there is all-composite..."
Click here and here for pics and details about the vehicle, but unrelated to how it may or may not be in the movie.
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