He certainly has enough motor to pull the KZ. Max weight fully loaded on that trailer is only 8800lbs, which amazes me for being over 30 feet long. You would want a TW of 900lbs to 1200lbs when fully loaded...That would give your the 10 to 15% recommended TW. KZ is long but when you are looking for a walk around bed (murphy bed is kinda cool never seen that before) and a enclosed garage it's going to be long. If trading in the new 1500 is not a option add some airbags. They will level and firm up the ride. With a good WDH with anti sway I think he would be good...
http://media.gmc.com/media/us/en/gmc/news.detail.html/content/Pages/news/us/en/2014/Jun/0619-gmc-sierra1500.html
