I have a 2013 Suburban LTZ. It booked out with options, low mileage at 18K between $37-$42. I bought it from my boss and took it off his hands for much less than that. I have seen the same model on the lot down the road (not sure on mileage but it an LTZ WDT just like mine) with a sticker for $39K.
I saw a Denali the other day, give or take a year, black, unknown mileage for $42K. So they are just taking the top of the range blue book and seeing if someone will bite. That is low mileage but like the guys said, you are close to new truck pricing overall. Should come down a bit and see what comps are around town. Good luck man.