Seems like a nice truck at 9k .
I think it was just a typo ..... The GCWR is usually the truck plus a trailer ? 26,000 lbs.
16,400 or so is the GVWR .
Like as suggested, adding some weight to the front portion (between the cab and camper) sounds like a good idea (water tank ).
It all boils down to your original question, is the COG too far back .
Yes the truck will handle the weight and be under the gross but i think its going to depend where you carry that weight . When you see 450 flatbed tow trucks hauling vehicles on the bed are they centered or are they more rearward ? It might make a difference in the handling to the point where its not comfortable .
I would ask someone that owns a 450 flatbed tow truck who hauls that kind of weight around on a regular basis, if the COG would create a handling issue if a full sized 5000# vehicle was flatbedded rearward the distance you state . (opposed to mid bed)
Maybe it would...maybe not . But i think it would answer your question and take the quesswork out of it .
http://www.allpar.com/trucks/chassis-cab.html