According to the specifications page, it is 11'11" tall. If you've installed an AC unit on the front, it will be taller. I'd suggest you measure it with it actually hooked to your truck because individual settings such as hitch height, tire size, etc can all come into play.
I agree, take your own measurements while hooked to your truck on a level surface. And take a measurement from the highest point that way you know your exact height in yours. I used a 2x4 leveled across the top of my AC where it hanged off the end of the roof, dropped a tape measure down to the ground up to the bottom of the 2x4 and added 1" for good measure.